Astrophysics of Galaxies
Overmassive supermassive black holes in SDSS close galaxy pairs
Maggie C. Huber, Julia M. Comerford and Joseph Simon
Supermassive black holes (SMBHs) and their host-
galaxies coevolve through channels such as hierarchical merging and AGN feedback, establishing tight scaling relations between SMBH masses and properties of the host-
galaxy. These scaling relations, particularly those with host-
galaxy bulge mass (M${_\text{b}}$) and stellar velocity dispersion ($\sigma$), are widely used to estimate SMBH masses.
Galaxy mergers drive gas into the centers of
galaxies, enhancing SMBH growth and stellar bulge growth but not necessarily in tandem, so it is necessary to determine if
galaxies undergoing a merger still follow SMBH-host-
galaxy scaling relations. In this study, we explore scaling relations in
galaxy mergers by taking advantage of the well-established value-added catalogs in the Sloan Digital Sky Survey. These catalogs provide close
galaxy pairs, AGN broad lines for SMBH mass measurements, and bulge-disk decomposed stellar masses. We compare SMBH mass estimates from M$_\bullet-$M${_\text{b}}$ to SMBH mass estimates from AGN broad lines and find that SMBH mass growth outpaces the bulge for AGN residing in the secondary (less massive) bulge and for smaller physical separations between
galaxies in a pair. Using our full sample of close
galaxy pairs, we find that M$_\bullet-$M${_\text{b}}$ and M$_\bullet- \sigma$ predict significantly different fractions of major and minor black hole mergers with M$_\bullet-$M${_\text{b}}$ predicting black hole mass ratios closer to 1:1 and $6-20\%$ more major mergers overall. These results have major implications, including for predictions of astrophysical gravitational-waves and high-
redshift overmassive SMBHs.
Read the full abstract ▾
Astrophysics of Galaxies
Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). V. The chronological merger tree of the Milky Way
Fernando Aguado-Agelet, Chiara Zerbinati, Davide Massari et al. (+9 more)
We present a new age determination of 24 globular clusters (GCs) dynamically associated with the main
accretion events experienced by the Milky Way (MW), as part of the Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) project's effort to trace the
Galaxy's assembly history. We used deep and homogeneous archival Hubble Space
Telescope data, and applied the CARMA isochrone-fitting code to derive homogeneous estimates of age,
metallicity, reddening, and distance modulus for systems dynamically associated with Gaia-Sausage-Enceladus (GSE), the Sagittarius dwarf
galaxy (Sag), the Helmi streams (H99), and the Sequoia
galaxy (Seq). These 24 new determinations are supplemented by 11 previously studied GSE clusters to construct the complete age-
metallicity relation (AMR) of the GSE system. We find that each progenitor system describes a well-defined AMR, with a distinct slope and extent reflecting its individual
star-formation efficiency and chemical enrichment history. By fitting analytical AMR models within a Markov chain Monte Carlo framework, we quantify the stellar mass and
accretion time for each progenitor
galaxy. This results in the first detailed merger tree obtained from strictly homogeneous chronological information, according to which the Low-energy-Kraken-Heracles (LKH) system is the first merger experienced by the MW that brought GCs in, followed by Sequoia, H99, GSE, and finally Sgr. The most significant events in terms of stellar mass are LKH, GSE, and Sgr, which together contribute a total of approximately 2.5 x 10^9 solar masses. This corresponds to more than 95% of the stellar mass accreted by the MW from mergers massive enough to host GCs.
Read the full abstract ▾
All authors Fernando Aguado-Agelet, Chiara Zerbinati, Davide Massari, Matteo Monelli, Santi Cassisi, Cristiano Fanelli, Carme Gallart, Edoardo Ceccarelli, Yllari Kay González Koda, Tomás Ruiz-Lara, Sara Saracino, Maurizio Salaris
Astrophysics of Galaxies
Why is there cold gas inside the Local Bubble?
Tim-Eric Rathjen and Jeffrey L. Linsky
The Local Bubble (LB) extends approximately 100–200~pc from the Sun and contains $10^6$~K
plasma and warm photoionised gas. Yet the Local Leo Cold Cloud (LLCC) and the Local Ribbon of Cold Clouds lie only 11–24~pc away, well inside the LB, at temperatures near 20~K. How such cold material forms and survives in this hotter environment remains uncertain, and explanations based on colliding warm clouds are difficult to test observationally. We investigate whether LLCC-like gas can assemble locally in a feedback-driven environment or must be imported as pre-existing cold material, and whether it can survive for several Myr. We use magnetohydrodynamic simulations from the SILCC Project including self-consistent
star formation, stellar winds and
supernovae, ionising and far-ultraviolet radiation, non-
equilibrium chemistry, and
cosmic-ray transport. We identify cold diffuse gas with $T<100$~K and $0<n_\mathrm{H_2}\leq2$~cm$^{-3}$ and use Lagrangian tracers to reconstruct its assembly, cooling, survival, and dispersal. The simulations produce cold diffuse gas in warm–hot, feedback-driven surroundings, where non-thermal pressure support is crucial.
Cosmic-ray pressure remains nearly continuous across cold-gas interfaces and establishes a pressure floor, while
magnetic pressure partly offsets the external thermal-pressure excess. The structures persist in the cold diffuse phase for a median of 2.5~Myr, and most of their material remains cold after they lose spatial coherence. The gas can assemble locally from nearby cold and thermally unstable warm material, developing filamentary or sheet-like morphologies. Cooling to $\sim20$~K is driven not by adiabatic expansion but by non-adiabatic cooling. The LLCC therefore need not have entered the LB as an already-formed cold cloud. LLCC-like gas can instead assemble and cool non-adiabatically in situ.
Read the full abstract ▾
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Formation of black hole stars via star–black hole collisions
Yanlong Shi, Qingru Hu, Zhenghao Xu et al. (+2 more)
In dense stellar environments such as globular clusters and active galactic
nucleus (AGN) disks, stellar-mass black holes (sBHs) may frequently collide with massive
stars. We investigate this process using semi-analytic models, three-dimensional hydrodynamical simulations, and one-dimensional stellar
evolution calculations, focusing on collisions between sBHs and a $100\,M_\odot$ main-sequence
star. We find that gas drag retains the BH within the stellar envelope unless the impact velocity exceeds $\sim2\sqrt{G(M_\star+M_\bullet)/R_\star}$. The post-collision outcome depends primarily on the BH-to-
star mass ratio. For $M_\bullet\gtrsim30\,M_\odot$, the retained envelope is either quasi-spherical or disc-like, but remains dynamically unstable because of shock heating. In contrast, for $M_\bullet\lesssim10\,M_\odot$, the collision forms a “black hole
star” (BH*): a quasi-hydrostatic, extended stellar envelope surrounding the embedded BH. These results agree with our analytic prediction that BH* formation necessarily requires $M_\bullet\lesssim0.2\,M_\star$. Follow-up MESA calculations further show that, for these low-mass BHs, the shock-heated remnant thermally relaxes without triggering runaway expansion. We discuss several astrophysical implications of BH*s, including their
evolution, the possibility of gravitational-wave events from BH binaries assembled within a stellar envelope, and repeated
star–sBH collisions as a pathway for rapid BH growth in dense stellar systems. This mechanism may contribute to the formation of massive BHs in high-
redshift nuclear
star clusters and may be relevant to the origin of the “little red dots” discovered by JWST.
Read the full abstract ▾
All authors Yanlong Shi, Qingru Hu, Zhenghao Xu, Douglas N. C. Lin, Norman Murray
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Dynamical formation of high-eccentricity compact binaries through BH–BH*/TZO collisions
Qingru Hu, Yanlong Shi, Douglas N. C. Lin et al. (+1 more)
The rapidly accumulating discoveries of binary stellar-mass black-hole (sBH) coalescences, detected by LIGO, have opened a new window into the formation and
evolution of compact binaries. In particular, residual orbital eccentricity may provide a distinctive signature of their formation channels. Here, we investigate a scenario in which high-eccentricity compact binaries form through the sequential capture of multiple sBHs by massive main-sequence
stars, using a combination of hydrodynamical and semianalytic few-body simulations. We find that sBHs with $M_\bullet\lesssim 0.2\,M_{\star}$ can be captured by massive
stars and settle into a quasi-hydrostatic black-hole
star (BH*) through gas dynamical friction. A subsequent encounter with a second sBH can then produce a compact binary embedded within the stellar envelope. Our hydrodynamical simulations show that through captures with small impact parameter, some binaries are born with high eccentricity ($e\gtrsim 0.5$), with its orbital frequency already entering the LISA band. Our semianalytic models further demonstrate that gas dynamical friction can pump the eccentricity to $e_{\rm 10\,Hz}>0.9$ before gravitational-wave emission eventually circularizes the binary during the final stage of coalescence. Once formed, the binary can merge quickly in $\sim 10$ hours. This channel may operate in dense stellar environments, such as
star clusters and active galactic
nucleus (AGN) disks. The same mechanism can also be applied to Thorne-Żytkow objects. A high-eccentricity binary in the LIGO band could therefore provide a distinctive signature of this formation scenario.
Read the full abstract ▾
All authors Qingru Hu, Yanlong Shi, Douglas N. C. Lin, Norman Murray
Astrophysics of Galaxies
The Limited Lifetime of Self-Gravitating Accretion Disks In Galactic Centers
Isaac Shlosman
Globally self-gravitating
accretion disks in active galactic
nuclei (AGN) have been frequently discussed in the literature, but never observed. Few dozen mega-masering
accretion disks in AGN have been detected, which display a clear Keplerian rotation on scales of 0.1-1 pc, allowing to estimate their masses within the sphere of influence (SoI) of the central supermassive black holes (SMBHs) to be smaller by more than a factor of 10, compared with the parent SMBH masses. Furthermore, the stellar components, deep inside the SoI, are dwarfed by the SMBH masses of M_BH ~ few X 10^6 - few X 10^7 Mo. Theoretically, no limit exists on sizes and masses of gaseous disks in AGN, which in principle, can exceed masses of their central compact objects. We analyze instabilities which can operate in gaseous disks, i.e., fragmentation for a locally dominant self-
gravity and spontaneous breaking of axial
symmetry for the globally self-gravitating disks. We invoke the gas response to the latter instability which leads to gravitational collapse, leaving a negligible mass behind and dynamically stable remnants. Consequently, the characteristic timescale for globally self-gravitating disks to exist in AGN should not exceed few rotations, t_phi ~ 10^{3-4} yrs for M_BH ~ 10^{6-8} Mo. Disk rebuilding is expected to be > 10^7 yrs, meaning that probability of finding is < 10^{-3}, which explains their lack of detection. We conclude that observed sub-parsec disks in AGN, at least the Keplerian masering ones, can be remnants of globally self-gravitating
accretion disks, and the instability timescale can be related to the duty cycle of AGN, t_duty ~ 10t_phi ~ 10^{4-5} yr.
Read the full abstract ▾
Astrophysics of Galaxies
Measuring Extragalactic Microlens Masses and Motions in Strongly Lensed Quasar Systems with Intensity Interferometry
Abigail Moran and Ken Van Tilburg
The direct measurement of masses and transverse motions of individual
stars and compact objects in distant
galaxies remains an outstanding challenge, leaving extragalactic stellar populations constrained only through model-dependent population fits. We show that time-resolved intensity interferometry of strongly lensed
quasars, combined with flux-ratio photometry, can break the source-size, microlens-mass, and transverse-velocity degeneracies of conventional light-curve microlensing. Using the quadruply lensed
quasar B1422+231 as a fiducial system and a next-generation interferometer ($\sim$800\,m$^2$ collecting area, spectral resolving power of 20,000, and few-picosecond timing), we forecast the precision on the
quasar source size and on the mass, position, and transverse motion of an individual stellar-mass microlens in the lens
galaxy. A single epoch determines the
accretion disk size to $4\%$ in favorable geometries ($10\%$ for a typical detectable configuration) and the microlens mass to order unity for $m_l \gtrsim 0.1\,M_\odot$. An eight-year, 33-epoch campaign reaches $\lesssim1\%$ on the disk size, localizes the microlens' impact parameter to $\sim0.1$-$0.5,\mu\mathrm{as}$, and resolves its proper motion. Such observations would enable direct measurements of individual extragalactic compact-object masses and transverse motions at moderate
redshift. They also yield sub-$\mu\mathrm{as}\,\mathrm{yr}^{-2}$ sensitivity to light-centroid acceleration, which can help separate stellar microlensing from dark matter substructure
lensing, the subject of a companion paper.
Read the full abstract ▾
Astrophysics of Galaxies
Dust and PAHs in late-stage galaxy evolution: Imprints of TP-AGB dust injection, grain growth and AGN feedback in high-z quiescent galaxies with JWST and ALMA
D. Donevski, A. Nanni, K. E. Whitaker et al. (+9 more)
A major unknown in late-stage
galaxy evolution is what regulates the cold interstellar medium (ISM) after quenching, a question central to interpreting molecular gas, dust, and stellar content in quiescent
galaxies (QGs) now probed by ALMA and JWST to $z\sim7$. We present the first semi-analytic model that follows the coupled post-quenching
evolution of dust, cold gas, and polycyclic aromatic hydrocarbons (PAHs), using flexible
star-formation histories and a framework tracking small and large carbonaceous and silicate grains. At $z\sim1$, we find that QGs of similar mass ($M_\star\sim8\times10^{10} M_\odot$), stellar-population age ($\sim2$ Gyr), and cold gas fractions ($f_{\rm gas}\sim1$-$10\%$), span $2$-$3$ dex in $M_{\rm dust}/M_\star$ and $M_{\rm dust}/M_{\rm gas}$, ranging from
star-forming-like ratios to highly depleted dust states. The diversity arises from delayed dust injection by thermally pulsing asymptotic giant branch (TP-AGB)
stars and ISM grain growth, which sustain dust enrichment for up to $\sim2.5$ Gyr after quenching. Without these channels, the pre-quenching $M_{\rm dust}$ falls below $10\%$ of its initial value within $\lesssim0.5$-$1$ Gyr, and twice as fast when AGN feedback is active. The imprint of post-quenching dust processing persists in substantial reservoirs of small carbonaceous grains, with PAH fractions of $\sim2$-$3\%$, even if the cold-dust budget falls below typical ALMA continuum detection limits ($M_{\rm dust}/M_\star\lesssim10^{-4}$). Such signatures may remain detectable with JWST/MIRI at $\mu$Jy depths, probing chemically enriched dust phases in otherwise ALMA-faint
galaxies. Altogether, dust and PAHs provide independent probes of distinct stages of ISM
evolution in QGs, rather than simply tracing the residual cold ISM of the preceding
star-forming phase.
Read the full abstract ▾
All authors D. Donevski, A. Nanni, K. E. Whitaker, A. W. S. Man, A. Faisst, A. Lapi, I. García-Bernete, M. Romano, T. Petrushevska, G. Gururajan, G. Lorenzon, D. Narayanan
Astrophysics of Galaxies · Cross-listed from astro-ph.CO
TDCOSMO. XXVII. JWST-based Lens Models and H$_0$ Measurement of WFI2033, HE0435, and PG1115
D. M. Williams, T. Treu, D. P. Johnson et al. (+13 more)
Time-delay cosmography offers a one-step, distance-ladder-independent route to the Hubble-Lemaitre constant, H_0. We present new cosmography-grade lens models of three quadruply imaged
quasars based on JWST-NIRCam/F115W imaging (WFI2033-4723, HE0435-1223, PG1115+080). We use the STARRED modeling technique, introduced in our previous analysis of WFI2033-4723, to reconstruct the complex JWST-NIRCam Point Spread Function at high fidelity. We combine NIRCam-based lens models with improved external convergence estimates, published time delays, and aperture-integrated stellar velocity dispersions from JWST NIRSpec to infer H_0. The analysis was carried out blindly for HE0435-1223 and PG1115+080, while it was not blind for WFI2033-4723, as we build upon the previous published model. For comparison with previous HST-based work, we limit our analysis to the case of no internal mass-sheet degeneracy ($\lambda_{\rm int}=1$). We quantify the impact of improved imaging, single-aperture kinematics, and environment measurements on central values and uncertainties. Within flat $\Lambda$CDM, assuming a uniform prior on $\Omega_{\rm m}$, we find H_0 = 71.8$_{-7.0}^{+9.2}$ $\lambda_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$ for PG1115+080, 74.2$_{-4.2}^{+4.2}$ $\lambda_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$ for HE0435-1223, and 73.4$_{-4.4}^{+3.4}$ $\lambda_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$ for WFI2033-4723. Combining the three lenses yields H_0 = 73.5$_{-2.8}^{+2.7}$ $\lambda_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$, consistent with HST-based results (73.6$_{-2.6}^{+2.6}$ $\lambda_{\rm int}$ km s$^{-1}$ Mpc$^{-1}$), but with reduced scatter between the three systems. These models will be incorporated in the TDCOSMO-2026 milestone paper with free $\lambda_{\rm int}$ in a hierarchical fashion. We close by outlining how 16 forthcoming JWST NIRCam targets will further tighten uncertainties toward percent-level precision on H_0.
Read the full abstract ▾
All authors D. M. Williams, T. Treu, D. P. Johnson, P. Mozumdar, S. Knabel, S. Birrer, C. D. Fassnacht, A. Galan, A. J. Shajib, K. C. Wong, M. Cappellari, F. Courbin, T. Morishita, V. Motta, D. Sluse, M. Stiavelli
Astrophysics of Galaxies
Resolved Dust in $z\approx1$ Galaxies with JWST/MIRI MRS: Survey Description and First View on PAHs, Mid-IR Atomic Emission, and Warm H$_2$
Wuji Wang, Andreas L. Faisst, Thomas S.-Y. Lai et al. (+16 more)
Dust is a key component of
galaxies that regulates their thermal balance and, consequently,
star formation and the build-up of stellar mass. Polycyclic aromatic hydrocarbons (PAHs) are responsible for reprocessing radiative energy of the
galaxies thus tracing dust
evolution. Using JWST/MIRI MRS, we present the first resolved view of the PAHs and mid-infrared emission lines in a sample of eight $z\approx1$
galaxies. A key novelty is our ability to directly map PAH emission near the end of
cosmic noon at JWST's limits. The sample is selected to be on the
star-forming main-sequence with stellar masses $M_{\star}=10^{10.6-11.2}\,M_{\odot}$ and infrared luminosities $L_{\rm IR}=10^{11.5-11.9}\,L_{\odot}$. Two of them contain active galactic
nuclei (AGN), and two are interacting systems. We detect and quantify primary PAH emissions from 3.3$\,\rm \mu m$ to 11.3$\,\rm\mu m$ throughout the
galaxies, alongside atomic fine structure lines (Ar, Ne, and Fe), Br$\alpha$, and H$_{2}$ rotational transitions. Through PAH ratio diagnostics and comparison to theoretical models, we qualitatively probe the physical properties of PAH molecules, i.e., size and charge. The AGN and mergers in our sample exhibit a higher fraction of neutral PAHs, possibly related to high radiation intensity and/or shocks, as suggested by increased atomic and H$_{2}$ line ratios. Leveraging the IFU data, we find that the grain sizes of the centrally located PAHs tend to be larger and less ionized than those in the outskirts of the
galaxies. Finally, we compare our results to observations of PAHs in local and similar-
redshift galaxies, revealing a potential evolutionary trend when controlling $L_{\rm IR}$.
Read the full abstract ▾
All authors Wuji Wang, Andreas L. Faisst, Thomas S.-Y. Lai, Kyle Finner, Jed McKinney, Andrew J. Battisti, Irene Shivaei, Leindert A. Boogaard, Daizhong Liu, Yu-Heng Lin, Lun-Jun Liu, Georgios Magdis, Vincenzo Mainieri, Alexander Rodriguez, John D. Silverman, Zhaoxuan Liu, Minju M. Lee, Ghassem Gozaliasl, Maximilien Franco
Astrophysics of Galaxies · Cross-listed from astro-ph.CO
Discovering Substellar Dark Matter Halos with Astrometric Weak Lensing of Multiply Imaged Quasars
Ken Van Tilburg and David E. Kaplan
We propose time-domain astrometric weak
lensing of multiply imaged
quasars as a probe of substellar dark matter (DM)
halos. In $\Lambda$CDM, each macro-image's light traverses many microhalos, producing a
stochastic centroid motion with a calculable red power spectrum.
Halos with crossing times longer than the survey impart a relative angular acceleration between image pairs. The response peaks at subhalo scale radii 0.005-2 pc and masses $3\times10^{-6}$-$10^2\,M_\odot$, 12-14 orders of magnitude below the smallest detected DM structures, down to the damping cutoffs of a 100 GeV thermal relic. We forecast the sensitivity of ten-year campaigns with 300 epochs for two
benchmark systems: the
galaxy-lensed quadruple B1422+231 at a 0.1 $\mu$as per-epoch precision forecast for extended-path intensity correlation, and the cluster-lensed triple SDSS J1029+2623 at 1 $\mu$as. The angular-acceleration channel reaches the standard $\Lambda$CDM microhalo population with a variance signal-to-noise ratio of order ten for the
galaxy lens (order unity after stellar microlensing subtraction) and 0.35 for the cluster under the optimistic assumption that 10% of the projected mass density at the image positions resides in surviving microhalos. A positive detection would: raise universal lower bounds on the DM particle mass to $\gtrsim400$ keV for
fermions and $\gtrsim10^{-12}$ eV for
bosons; constrain the DM kinetic decoupling temperature to $\gtrsim 10$ MeV; and be sensitive to the running of the spectral tilt at the 0.01 level over 15-20 e-folds of the primordial
curvature power spectrum. A robust null result across well-characterized lenses would constrain microhalo survival and/or imply violations of the above inequalities. These signatures motivate differential astrometric observations with extreme 0.1-1 $\mu$as light-centroiding precision on multiply imaged
quasars. [Abridged]
Read the full abstract ▾
Astrophysics of Galaxies
Map of the Interstellar Continuum FUV Field within 800 Parsecs
David Lomeli, Kedron Silsbee, Alexei Ivlev et al. (+1 more)
The far-ultraviolet (FUV) field, consisting of
photons with energies between 6 and 13.6 electron volts, plays an important role in the chemical and thermodynamical
evolution of the interstellar medium. FUV continuum radiation is produced by bright
stars in the
galaxy and absorbed by interstellar dust. We used newly available maps of the dust distribution, in conjunction with catalogs of stellar positions and spectra, to create a map of the stellar FUV field within 800 parsecs of the Earth. The map shows a total FUV intensity in the solar neighborhood in line with existing measurements (0.7 times the Draine field), but substantial point-to-point fluctuations exist. Near the Galactic midplane, the FUV intensity decreases with increasing gas density up to a density of approximately 10 hydrogen atoms per cm$^3$, due to absorption of light by dust. Between 10 and 50 hydrogen atoms per cm$^3$ the UV field increases again, due to a positive correlation between high density gas and young hot
stars. We find that the spectrum is generally harder where the UV field is higher, and softer in regions where dust extinction is more important. The resulting map, as well as our catalog of derived stellar properties, are both available for download for those wishing to study a nearby region of the ISM.
Read the full abstract ▾
All authors David Lomeli, Kedron Silsbee, Alexei Ivlev, Marta Obolentseva
Astrophysics of Galaxies
LightCube: A Parsec-Resolution 3D Model of the Local Far-Ultraviolet Interstellar Radiation Field
Hannah V. Bish, J.E.G. Peek, Catherine Zucker et al. (+5 more)
We present a three-dimensional model of the local interstellar radiation field (ISRF) in the ultraviolet (UV). Using UV flux measurements from the TD1 catalog and stellar distances from Gaia and Hipparcos, we construct a catalog of
stars that we expect to dominate the UV flux in the nearby
Galaxy. We use the radiative transfer code DIRTY to model the propagation of
photons from these
stars through a 3D dust map, including the effects of scattering and absorption. The result is LightCube, a model of the ultraviolet ISRF out to 1.25 kpc from the Sun, with a maximum linear resolution of 1 pc. We model the ISRF in the four TD1 bands (1565 A, 1965 A, 2365 A, and 2740 A), as well as a single value for the full FUV range, and calculate the ISRF at the Sun to be 5.65$\times$10$^{-14}$ erg cm$^{-3}$ from 912 A to 2000 A. The modeled ISRF is quite variable, with more than an order of magnitude variation seen in dense regions, and about half that in lower density regions. By comparing LightCube to an estimate of the 3D distribution of total-to-selective extinction ratio, $R_V$, we find a positive correlation between UV flux and $R_V$ in regions of low UV radiation.
Read the full abstract ▾
All authors Hannah V. Bish, J.E.G. Peek, Catherine Zucker, Karl D. Gordon, Claire E. Murray, Susan E. Clark, Mathieu Willems, Erika Hamden
Astrophysics of Galaxies
Non-isothermal vertical distribution functions for the Milky Way
Maria Djurić and Ralph Schönrich
The vertical structure of our
Galaxy has commonly been assumed to follow a pseudo-isothermal distribution. However, there is no a priori reason to expect this form to arise from scattering by giant molecular clouds (GMCs), since GMCs are confined to a narrow layer around the Galactic midplane and therefore do not randomise
stars uniformly in vertical phase space. We first present a simple statistical argument to derive a new vertical distribution function (DF), in the limiting case of a razor-thin distribution of GMCs, which admits an extra factor of ${J_z}^{-\alpha}$, where $\alpha>0$ and varies for different potentials. In light of this, we revisit the
diffusion coefficients for vertical heating from the mechanics of two-body scattering, in a more realistic, extended distribution of GMCs. The resulting drift and
diffusion coefficients are strongly non-linear in $v_z$, particularly at low relative velocities, where the effective range of weak, local encounters can vanish. We determine stationary solutions, and also numerically solve the orbit-averaged Fokker–Planck equation with time-dependent coefficients. We find, in both cases, a vertical action distribution that deviates from that of the pseudo-isothermal case, and propose a new, family of vertical DFs that generalise the pseudo-isothermal form. We find the two primary
agents of non-isothermality are: (i) a GMC distribution confined near the midplane, and (ii) the fact that the Coulomb logarithm, $\Lambda$ is strongly velocity-dependent at small velocities, and cannot be treated as a constant, contrary to the commonly adopted assumption.
Read the full abstract ▾
Astrophysics of Galaxies
$N$-body simulations of the open cluster population in the Milky Way and the impact of GMC encounters
Timmi G. Jørgensen and Ross P. Church
We investigate the population of open clusters in the Solar Neighbourhood and model the effect of encounters with giant molecular clouds (GMCs) over the last 1 Gyr. We combine a Galactic model with $N$-body simulations of 20692 unique clusters in the mass range $[50-24000]$ $\mathrm{M}_{\odot}$. Each cluster is simulated twice: with and without tidal forces from the GMCs. We find that an initial cluster mass function truncated at $\sim 9000$ $\mathrm{M}_{\odot}$ best reproduces the observed mass function
evolution. For the age function, the observations show a decline in clusters for ages older than $\sim 1$ Myr, whereas our simulated clusters show a decline after $\sim 50$ Myr. The observed early disruption suggests that some clusters form supervirial, whereas our simulated clusters are created in virial
equilibrium. Low-mass ($<600 \, \mathrm{M}_{\odot}$) clusters are most sensitive to GMC encounters, which accelerate their disruption in the first $\sim 200$ Myr. After $\sim 500$ Myr, the impact of GMCs becomes irrelevant since the clusters will have been destroyed regardless of whether they experience GMC encounters or not. The survival of intermediate-mass ($600-6000\, \mathrm{M}_{\odot}$) clusters is significantly reduced by GMCs at ages up to 1 Gyr. High-mass ($>6000 \, \mathrm{M}_{\odot}$) clusters survive to 1 Gyr with minimal disruption with or without GMCs. We find that clusters that have had strong GMC encounters within the last $20$ Myr should have tidal tails that are randomly orientated with respect to the Galactic centre.
Read the full abstract ▾
Astrophysics of Galaxies
Exploring the survivability of higher-order multiple protostellar systems – The case of VLA1623
N. M. Murillo and A. Pérez-Villegas
Higher-order protostellar systems ($\geq$3 components) are commonly observed in the early stages of low-mass
star formation. A persistent question in
star formation and
evolution is whether these higher-order protostellar systems survive as gravitationally bound systems or dissolve into binaries over time. We explore this question with a case study of the embedded quadruple protostellar system VLA1623 and its observational constraints, assuming that the components A1, A2, B, and W are gravitationally bound. Using $N$-body simulations, we run a grid of models considering
gravity, mass
accretion onto protostars, the presence of the protostellar cloud core, and its dispersal. The simulations are integrated over a period of 8 Myr to take into account the
evolution from the protostellar phase (Class 0 and I, 1 Myr), through the pre-main sequence (Class II and III, 2 – 3 Myr), and into the main sequence (4 Myr). Our results show that VLA1623 has a probability of 30% to remain as a gravitationally-bound quadruple system up to 8 Myr from the current state. There is also a 25–30% probability of VLA1623 dissolving into a triple system. This suggests that the dissolution of quadruple protostellar systems contributes to the formation of stable triple (proto)stellar systems. Components A1 and A2 are the most likely to be ejected, while W has a lower probability of being ejected from the system. The stability of VLA1623 depends on a combination of component mass ratios wrt the primary, separations, and eccentricities.
Read the full abstract ▾
Astrophysics of Galaxies
Revisiting the enigmatic sixth star cluster in the Fornax dwarf spheroidal galaxy
Chiara Crociati, Annette M. N. Ferguson, Raffaele Pascale et al. (+7 more)
The Fornax dwarf spheroidal (dSph)
galaxy is one of only two Local Group dSphs that host a population of globular
star clusters (GCs), the present-day properties of which have often been used to investigate the nature of the dark matter. An additional overdensity of
stars called Fornax 6, lying at a projected distance of $\sim$0.3 kpc from the
galaxy centre, was recently identified as a sixth GC residing in Fornax. However, this conclusion was based on shallow, low-resolution photometric observations and a limited number of spectra. Here, we reinvestigate the nature of Fornax 6 by analysing MUSE/Wide-Field-Mode observations alongside deep GMOS-S imagery. Using a sample of 132 spectra of red giant and horizontal branch
stars, we confirm the Fornax 6 overdensity as a distinct chemo-dynamical component with respect to the surrounding field population. Specifically, we identify 43 likely members associated with the cluster, from which we measure $\rm [Fe/H] =-0.61\pm0.03\,$dex, $v_{\rm los} = 50.9^{+0.8}_{-0.7}\,\rm km \,s^{-1}$, $\sigma_v = 3.2^{+1.4}_{-1.5}\,\rm km \,s^{-1}$. The main-sequence turn-off, observed here for the first time, strongly suggests that these
stars are coeval and well described by a $\sim$3 Gyr old isochrone. The cluster is characterised by an irregular morphology, a large half-light radius ($R_{h}=8.8^{+1.1}_{-1.3}\,$pc), a small flattening ($e=0.14^{+0.12}_{-0.10}$), and low luminosity ($M_{V} = -5.0 \pm 0.4$). Our improved characterisation of Fornax 6 supports its classification as a genuine low-mass cluster likely undergoing tidal disruption, making it the youngest and most metal-rich member of Fornax's unique GC system.
Read the full abstract ▾
All authors Chiara Crociati, Annette M. N. Ferguson, Raffaele Pascale, Sebastian Kamann, Silvia Martocchia, Jess M. Howell, Pete B. Kuzma, Dougal Mackey, Sakurako Okamoto, Masato Onodera
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
Bright Metal-Poor Star Survey - I. Tomo-e Gozen narrow-band photometric survey and medium-resolution spectroscopic follow-up
Hiroko Okada, Takumi Iwasaki, Nozomu Tominaga et al. (+21 more)
We present the Tomo-e Gozen Bright Metal-Poor
Star Survey (TeMPS), a wide-area narrow-band photometric survey for bright metal-poor
stars in the northern sky. The survey uses the Tomo-e Gozen camera on the 1.05 m Kiso Schmidt
telescope with four narrow-band filters centered on the \ion{Ca}{2} H and K lines, the CH $G$ band, H$\alpha$, and a reference wavelength region. We review the survey strategy, photometric processing, and calibration of
metallicity and carbon abundance estimates derived from narrow-band colors. We further present medium-resolution spectroscopic follow-up with Nayuta/MALLS to validate the photometric selection and identify new metal-poor
stars. The current data set covers $\gtrsim 22,000$d̃eg$^{2}$ in all four bands with a total integration time of $\sim 100$ hr. The median limiting magnitudes at S/N = 20 correspond to $G\sim12.5$. By combining narrow-band photometry with archival broad-band photometry and Gaia distances, we estimate $T\_{\rm eff}$, $\log (g)$,
metallicity, and carbon abundance. Calibration against literature abundances derived from high-resolution spectra shows typical scatters of $< 0.3$ dex in
metallicity and $< 0.4$ dex in carbon abundance. We estimate
metallicities for $\sim 1.7$ million
stars and identify $\sim 16,000$ very metal-poor candidates with [M/H]$_{\rm NB,fin}<-2$. We show that Nayuta/MALLS medium-resolution spectra provide
metallicities consistent with high-resolution measurements, with a scatter of $\sim 0.27$ dex. Among 32 photometrically selected candidates followed up with MALLS, 24 are confirmed to have [M/H]$_{\rm MALLS}< -2$, including one newly identified
star with [M/H]$_{\rm MALLS}\simeq -3.4$. These results demonstrate that Tomo-e Gozen narrow-band photometry and MALLS medium-resolution spectroscopic follow-up efficiently select bright metal-poor
stars for future high-resolution abundance studies. (abbreviated)
Read the full abstract ▾
All authors Hiroko Okada, Takumi Iwasaki, Nozomu Tominaga, Wako Aoki, Satoshi Honda, Kurumi Furutsuka, Tadafumi Matsuno, Tomoki Morokuma, Takuma Suda, Miho N. Ishigaki, Naoto Kobayashi, Hidenori Takahashi, Yuu Niino, Satoshi Takita, Sohei Kondo, Yuki Mori, Kenzo Kinugasa, Shigeyuki Sako, Tomio Kanzawa, Hikaru Iwashita, Kenji Mitsui, Takeo Fukuda, Keiko Kaneko, Mitsuhiro Fukushima
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
NGTS clusters survey - VI: Stellar rotation in seven young open clusters within the PLATO LOPS2 field
Alexander Hughes, Edward Gillen, Matthew Battley et al. (+18 more)
We present NGTS measurements of rotation period distributions for FGKM
stars in seven young open clusters spanning ~40–700 Myr within PLATO's first long-stare LOPS2 field. We measure 1063 rotation periods, of which 479 are newly analysed as part of cluster specific rotation studies, whilst 63 are unique periods not reported in the recent TESS All-Sky Rotation Survey. Of the 1063 rotation periods, 285 are identified as likely binary or higher order multiple systems using colour-magnitude diagrams and Gaia astrometry. These are the first comprehensive rotation period distributions for Trumpler 10, NGC 2451B and Alessi 3, while extending existing distributions for NGC 2451A, NGC 2516, Collinder 135 and IC 2391, to create a fuller picture on the rotation state of young
stars in PLATO's LOPS2 field. We find that main-sequence solar-mass
stars in the ~40 Myr old NGC 2451B cluster, form a slow sequence that can be distinguished from their counterparts at ~70–80 Myr, thereby significantly reducing the age at which young stellar groups can be relatively aged via their rotation sequences. We also observe stalled
spin down from the age of NGC 2451A to at least that of NGC 2516 (~70–150 Myr) at masses $\gtrsim1$ $M_{\odot}$, supporting previous predictions that angular momentum redistribution and removal should result in a wave of stalled
spin down that propagates as a function of both mass and age. Finally, we provide a new age estimate for Alessi 3 of 687$\pm$106 Myr using differential gyrochronology age dating.
Read the full abstract ▾
All authors Alexander Hughes, Edward Gillen, Matthew Battley, Deepak Chahal, Beatrice Caccherano, David Anderson, Ioannis Apergis, Daniel Bayliss, Matthew Burleigh, Jorge Fernández Fernández, Michael Goad, George Harvey, James S. Jenkins, Alicia Kendall, James McCormac, Jose Moyano, Gavin Ramsay, Suman Saha, Jose Vines, Richard G. West, Peter J. Wheatley
Astrophysics of Galaxies
HURACAN: A comparison of stellar and interstellar proper motions inside L1688
M. Piecka, J. Alves, A. Rottensteiner et al. (+3 more)
The assumption that molecular clouds are kinematically coupled to the young stellar populations forming within them is observationally still poorly constrained. With the transverse component $v_{\textrm{t}}$ of the interstellar medium (ISM) motion being largely unknown, the three-dimensional kinematic state of even the closest clouds remains incomplete. We provide the first direct measurement of the transverse motion of the ISM inside the Ophiuchus cloud L1688 and compare it with the kinematics of the surrounding young stellar populations. The measurement was obtained using intensity-based image registration applied to archival data, allowing us to generate a proper motion field of the studied regions and determine the cloud's bulk motion, $(\mu_{\alpha^*},\mu_\delta)^{\mathrm{ISM}}_{\mathrm{median}}=(-3.0, -24.1)$ mas yr$^{-1}$. This motion differs from the kinematics of the youngest population in Upper Scorpius by $3\pm1$ km s$^{-1}$, highlighting the possibility of a bias when using
stars as a proxy for the ISM motion near
star-forming regions. By comparing the cloud's motion with that of the youngest stellar population in the region and the B-
star Oph S1 located within the cloud, we find that stellar feedback must have dynamically shaped the motion of the ISM over the last few million years. Furthermore, by studying a shell-like ISM structure appearing in L1688, we find evidence suggesting that this object is likely neither a typical Herbig-Haro object nor a
supernova remnant, with its origin remaining a mystery. Our results demonstrate that archival and future high-resolution near-infrared observations can and will continue to enable measurements of ISM transverse motions in nearby clouds, opening a new window for studying ISM dynamics that is not accessible when using radial velocities alone.
Read the full abstract ▾
All authors M. Piecka, J. Alves, A. Rottensteiner, S. Hutschenreuter, S. Meingast, L. Posch
Astrophysics of Galaxies
The solitary star cluster of the Andromeda XXV dwarf spheroidal
Chiara Crociati, Annette M. N. Ferguson, Gracie McGill et al. (+6 more)
We present Hubble Space
Telescope Advanced Camera for Surveys observations of Gep I, a globular cluster (GC) candidate in the low-mass ($M_{\star}\sim 6.5 \times 10^5\,M_{\odot}$) M31 dwarf spheroidal (dSph) satellite Andromeda XXV (And XXV). We confirm the nature of this object and provide the first detailed characterisation of its resolved stellar populations using a colour-magnitude diagram (CMD) that reaches 2 magnitudes below the horizontal branch. We compare Gep I's
metallicity and distance with those of the surrounding And XXV stellar population, and find them to be strikingly similar, consistent with a physical association between the GC and the dSph. Gep I is very extended ($R_h=24^{+5}_{-4}$ pc) and faint ($M_V = -4.5 \pm 0.2$ mag), similar to the
star clusters residing in other low-mass dwarf
galaxies. It is characterised by a very low
metallicity ($\rm [Fe/H] = -2.4^{+0.3}_{-0.4}\,$dex) and a red horizontal branch morphology, a combination also seen in suspected accreted GCs in the M31
halo and in the Local Group dwarf irregular
galaxy NGC 6822. While Gep I is most likely a genuine
star cluster, the current data do not exclude the tantalising possibility that it consists of And XXV
stars temporarily captured by a dark subhalo orbiting within the dSph's potential well.
Read the full abstract ▾
All authors Chiara Crociati, Annette M. N. Ferguson, Gracie McGill, Raffaele Pascale, Anna Genina, Pete B. Kuzma, Dougal Mackey, Alan W. McConnachie, Rokas Žemaitis
Astrophysics of Galaxies · Cross-listed from astro-ph.SR
Carbon in J0815+4729: Casting a shadow of doubt on the interpretation of CH absorption in the most primitive stars
Junbo Zhang, Carlos Allende Prieto, Yeisson Osorio et al. (+7 more)
Aims. We revisit the carbon abundance in the primitive iron-poor
star J0815+4729 ([Fe/H] = -5.49). J0815+4729 is so carbon-enhanced and oxygen-rich that, in addition to CH and C2 molecular lines, weaker neutral atomic transitions are measurable in its spectrum, providing a unique opportunity to explore the line formation of C I and O I transitions in such an extremely iron-deficient
star. Methods. Based on high-resolution spectroscopy and newly constructed atomic models for carbon and oxygen, we present the first investigation to derive carbon and oxygen abundances of this hyper iron-poor
star from neutral atomic transitions under non-local thermodynamic
equilibrium (NLTE) conditions. Results. The carbon abundance derived from C I lines is A(C)NLTE = 8.08+-0.07, consistent with that inferred from C2 lines (A(C)LTE =7.96 +- 0.08), but around 0.6 dex higher than the value from CH lines (A(C)LTE = 7.47 +- 0.17). Since CH lines are the most commonly-used carbon abundance indicator for extremely metal-poor
stars, this result casts doubt on the quantitative interpretation of CH absorption in the most primitive
stars. We confirm that J0815+4729 is one of the most carbon-enhanced
stars with [Fe/H] <= -4.5 known to date. We have also determined A(O)NLTE as 7.25 +- 0.11, with NLTE corrections of around -0.11 dex. The carbon-to-oxygen ratio of the
star is [C/O] = 1.06 +- 0.1.
Read the full abstract ▾
All authors Junbo Zhang, Carlos Allende Prieto, Yeisson Osorio, Jonay I. González Hernández, David S. Aguado, Ivan Hubeny, Shuai Liu, Jianrong Shi, Rafael Rebolo, Gang Zhao
Astrophysics of Galaxies
SERENADE III: Insight into the Origin of the High Dust Temperature and High [O III]/[C II] Ratio at $z\gtrsim6$
Ikki Mitsuhashi, Yuichi Harikane, Hiddo S. B. Algera et al. (+10 more)
We present an analysis of ALMA high-frequency observations of nine bright Lyman-break
galaxies at $5.8<z_{\rm spec}<8.3$. Our sample consists of five
galaxies at $z\sim6$ newly observed in Band-9 and/or 10, allowing us to better constrain the dust temperature ($T_{\rm dust}$) in a statistical sample of $z\gtrsim6$
galaxies. Our measurements of the dust temperature at $z\sim6-9$ suggest most of the
star-forming
galaxies show $T_{\rm dust}\sim40\,{\rm K}$ on average, whereas three
galaxies show significantly higher $T_{\rm dust}$ ($\gtrsim60\,{\rm K}$). We find a potential negative correlation between $T_{\rm dust}$ and gas-phase
metallicity with $T_{\rm dust}\propto Z^{-0.50\pm0.19}$, implying decreased dust shielding and efficient dust heating in low-
metallicity environments. Given the systematic offset of $T_{\rm dust}$ between $z\sim0$ and $z\sim6-9$ at fixed
metallicity, we find $T_{\rm dust}$ is well described by sSFR as well as $Z$ with $\log T_{\rm dust}=-0.25^{+0.03}_{-0.04}\times(\log Z-0.57\times\log {\rm sSFR})+4.88^{+0.47}_{-0.43}$ across $z\sim0$ to $z\sim6-9$. Simultaneously with the dust continuum, these observations cover the [OI]63$\mu$m emission line for five
galaxies, which traces dense neutral gas. We find a lower [CII]/[OI] ratio in $z\gtrsim6$
galaxies than in local samples, suggesting that [CII] becomes fainter due to collisional de-excitation at high gas density. Combining the [OI], [OIII], and [CII] lines and cloudy modeling, our results imply $\log U_{\rm ion}\sim-2$ and $\log n_{\rm H}\,[{\rm cm}^{-3}]\sim2.5$ in $z\gtrsim6$
galaxies, which is $\sim3-10\times$ higher $U_{\rm ion}$ and $\sim2-3\times$ higher $n_{\rm H}$ than the local samples. The combination of these enhanced $U_{\rm ion}$ and $n_{\rm H}$ naturally explains the high [OIII]/[CII] ratio at $z\gtrsim6$.
Read the full abstract ▾
All authors Ikki Mitsuhashi, Yuichi Harikane, Hiddo S. B. Algera, Tom J. L. C. Bakx, Andrea Ferrara, Akio K. Inoue, Masatoshi Imanishi, Kotaro Kohno, Yoshiaki Ono, Yuma Sugahara, Hideki Umehata, Livia Vallini, Jorge A. Zavala
Astrophysics of Galaxies · Cross-listed from astro-ph.CO
ELUCID-DESI II. Revealing dark matter mass, tidal, and velocity (MTV) fields using galaxy group phase information
Qingyang Li, Xiaohu Yang, Wensheng Hong et al. (+24 more)
We introduce a novel method for reconstructing the
cosmic mass, tidal, and velocity (MTV) fields over the
redshift range $0 < z < 0.6$ using the phase information of
galaxy groups. This approach replaces the explicit theoretical bias correction typically needed to relate
galaxy groups to the underlying dark matter density field with a simulation-calibrated statistical mapping, reducing a major source of systematic uncertainty and making the method directly applicable to spectroscopic
redshift surveys such as the DESI Bright
Galaxy Survey (BGS). We evaluate the performance of our MTV reconstruction pipeline with mock
redshift surveys that include a comprehensive set of observational selection effects. The
galaxy groups used as tracers are identified with an extended
halo-based group finder applied to the DESI mock
galaxy catalogue with an apparent magnitude limit of $m_z < 19.65$, yielding a
galaxy number comparable to that of the DESI BGS faint sample ($m_r < 20.175$). Our tests show that the reconstructed velocities are accurate and unbiased, with a residual dispersion of $\sim 120\ \mathrm{km\,s^{-1}}$ across the
redshift bins. The recovered velocity field allows us to shift
galaxy groups to their real-space positions, thereby correcting for the Kaiser effect. By iteratively applying this Kaiser correction to the
galaxy groups, we further reconstruct the tidal field and the mass-density distribution. The reconstruction is stable with respect to the grid resolution. Overall, our results demonstrate that this group-based phase-space reconstruction provides a robust pathway to recovering the dark matter MTV fields, with strong prospects for application to DESI BGS data.
Read the full abstract ▾
All authors Qingyang Li, Xiaohu Yang, Wensheng Hong, Feng Shi, Youcai Zhang, Jiaqi Wang, Junde Li, Yiyang Guo, Yingxiao Song, Huiyuan Wang, Yan-Chuan Cai, Yizhou Gu, Chengze Liu, Jiaxin Han, Zhongxu Zhai, Yu Yu, Yipeng Jing, Houjun Mo, Yuyu Wang, Hao-Ran Yu, Yingjie Peng, Weiguang Cui, Qi Guo, Liang Gao, Xi Kang, Weipeng Lin, Jie Wang
Astrophysics of Galaxies · Cross-listed from astro-ph.HE
Optical Discovery of New and Candidate Galactic Supernova Remnants Plus Optical Imaging of the Monogem Supernova Remnant
Robert A. Fesen, Marcel Drechsler, Bray Falls et al. (+16 more)
We report the discovery of new and candidate Galactic
supernova remnants made through over 2000 hours of H$\alpha$ and [O III] imaging using amateur class instrumentation. These nebulae range from 0.5 to over 8 degrees in size. Five of these, namely G27.8-17.1, G115.6+9.2, G190.5+25.3, G195.9+2.2 and G239.9+7.0 exhibit low-dispersion optical spectra indicating shock emission by the presence of strong [S II] $\lambda\lambda$6716,6731 and [O I] $\lambda$6300 line emissions relative to H$\alpha$, or exhibit a nonradiative shock generated Balmer dominated spectrum. Their filamentary emission morphology also supports the presence of interstellar shock fronts. Three other optical nebulae, G191.3+11.1, G205.7-1.7, and G305.4-0.7 appear likely to be remnants and are proposed as new SNR candidates. We also present [O III] and H$\alpha$ images of optical filaments associated with the 25 degree diameter Monogem Ring SNR which reveal extensive emission-line filaments around most of the remnant's X-ray boundaries. Deep images of the X-ray suspected remnant G190.4+12.5 and the large and [O III] emission dominated SNR G206.6+6.1 seen toward or near the Monogem SNR are also included. Key findings of this work include: 1) optical surveys can sometimes detect SNRs better than
radio and X-ray SNR searches, 2) Balmer nonradiative shocks appear not uncommon in high Galactic latitude SNRs, and 3) faint Ø3 emission dominated SNRs may have been missed in prior H$\alpha$ emission only surveys.
Read the full abstract ▾
All authors Robert A. Fesen, Marcel Drechsler, Bray Falls, Tim Schaeffer, Justin Anderson, Deepanshu Arora, Werner Becker, Carl Bjork, Steeve Body, Laurent Huet, Tarun Kottary, Mathew Ludgate, Nicolas Martino, Manuel Peitsch, Wolfgang Reich, Jose Rodrigues, Yann Sainty, Patrick Sparkman, Sean Walker
Astrophysics of Galaxies
Visualizing Disequilibrium: Tracing Two-Point Correlations to Specific Spatial Structures in the Milky Way
Austin Hinkel and Josephine Vanzant
The Two-Point Correlation Function can be used to demonstrate the existence of substructure within a
dataset, but typical implementations do not track the individual points which contribute to each specific substructure. In this paper, we develop an
algorithm that traces a two-point correlation signal back to the contributions of each data point, allowing for structure to be visualized in novel ways. Using this tool, we find substantial evidence for pervasive spatial clustering in the Milky Way and reveal complex undulations that warp the previously discovered vertical density waves. We also explore the “clumping" of
stars in the thick disk and near-
halo regions and discuss the possibility of dating the structure.
Read the full abstract ▾