arXiv subjects

Scott Carlsten

Publications and source records attributed to Scott Carlsten.

9 recordsLinked to original sources

arXiv2026

A Sample of Nearby Isolated Dwarf Galaxies: A First Look at the Mass Function of Field Dwarfs

We present the results of the Exploration of Local VolumE Survey - Field (ELVES-Field), a survey of the dwarf galaxies in the Local Volume (LV; $D<10$ Mpc) over roughly $3,000$ square degrees, focusing on the field dwarf population. Candidates are detected using a semi-automated algorithm tailored for low surface brightness dwarfs. Using tests with injected galaxies, we show the detection is $50\%$ complete to $m_g\sim20$ mag and $M_\star \sim 10^6$ $M_\odot$. Candidates are confirmed to be true nearby dwarfs through distance measurements including redshift, tip of the red giant branch, and surface brightness fluctuations. We identify isolated, field dwarfs using various environmental criteria. Over the survey footprint, we detect and confirm 95 LV dwarfs, 44 of which we consider isolated. Using this sample, we infer the field dwarf mass function and find good agreement at the high-mass end with previous redshift surveys and with the predictions of the IllustrisTNG simulation. This sample of isolated, field dwarfs represents a powerful dataset to investigate aspects of small-scale structure and the effect of environment on dwarf galaxy evolution.

astro-ph.GA↗

arXiv2026

ELVES-Field: Isolated Dwarf Galaxy Quenched Fractions Rise Below $M_* \approx 10^7$ $M_\odot$

We use a new sample of low-mass ($M_* < 10^9$ $M_\odot$) isolated galaxies from the Exploration of Local VolumE Survey - Field (ELVES-Field) to examine the star formation properties and sizes of field dwarf galaxies in the Local Volume (LV; $D<10$ Mpc). This volume-limited sample was selected from nearly 3,000 square degrees of imaging, relying on surface brightness fluctuations to determine distances to the majority of the systems and is complete to $M_* \approx 10^6$ $M_\odot$. Across the surveyed area, we catalog over 2300 candidate LV dwarfs, of which we confirm 95 as genuine LV members and reject over 1600 as background contaminants, with the remaining 600 candidates still requiring a distance measurement. Of the confirmed LV dwarfs, 46 are either new discoveries or confirmed via a distance measurement for the first time here. We explore different environmental criteria to select isolated dwarfs but primarily focus on dwarfs that are $>2\times R_{\mathrm{vir}}$ in projection from any known group with $M_\star > 10^9$ $M_\odot$. We find that, at higher dwarf masses ($M_\star \gtrsim 10^7$ $M_\odot$), essentially all field dwarfs are star-forming as has been found before. In contrast, at $M_\star \lesssim 10^7$ $M_\odot$, $\sim30\%$ of field dwarfs appear to be quenched. Finally, we find that isolated dwarfs are noticeably smaller ($\sim 20\%$) than satellite dwarfs of the same stellar mass, regardless of quenched status.

astro-ph.GA↗

arXiv2025

A Possible "Too-Many-Satellites" Problem in the Isolated Dwarf Galaxy DDO 161

The abundance of satellite galaxies provides a direct test of $\Lambda$CDM and galaxy formation physics on small scales. While satellites of Milky Way-mass galaxies are well studied, those of dwarf galaxies remain largely unexplored. We present a systematic search for satellites around the isolated dwarf galaxy DDO~161 ($M_\star \approx 10^{8.4}\, M_\odot$) at a distance of 6 Mpc. We identify eight satellite candidates within the projected virial radius and confirm three new satellites through surface brightness fluctuation distance measurements from deep Magellan imaging data. Together with its confirmed satellite UGCA~319, DDO~161 has four confirmed satellites above $M_{\star}^{\rm sat} > 10^{5.4}\, M_\odot$, making it the most satellite-rich dwarf galaxy known to date. We compare this system with predictions from the TNG50 cosmological simulation, combined with currently established galaxy-halo connection models calibrated on Milky Way satellites, and find that DDO~161 has a satellite abundance far exceeding all current expectations. The rich satellite system of DDO~161 offers new insight into how low-mass galaxies occupy dark matter halos in low-density environments and may provide new constraints on the nature of dark matter.

astro-ph.GA↗

arXiv2022

ELVES IV: The Satellite Stellar-to-Halo Mass Relation Beyond the Milky-Way

Quantifying the connection between galaxies and their host dark matter halos has been key for testing cosmological models on various scales. Below $M_\star \sim 10^9\,M_\odot$, such studies have primarily relied on the satellite galaxy population orbiting the Milky Way. Here we present new constraints on the connection between satellite galaxies and their host dark matter subhalos using the largest sample of satellite galaxies in the Local Volume ($D \lesssim 12\,\mathrm{Mpc}$) to date. We use $250$ confirmed and $71$ candidate dwarf satellites around 27 Milky Way (MW)-like hosts from the Exploration of Local VolumE Satellites (ELVES) Survey and use the semi-analytical SatGen model for predicting the population of dark matter subhalos expected in the same volume. Through a Bayesian model comparison of the observed and the forward-modeled satellite stellar mass functions (SSMF), we infer the satellite stellar-to-halo mass relation. We find that the observed SSMF is best reproduced when subhalos at the low mass end are populated by a relation of the form $M_\star \propto M^\alpha_\mathrm{peak}$, with a moderate slope of $\alpha_\mathrm{const}=2.10 \pm 0.01$ and a low scatter, constant as a function of the peak halo mass, of $\sigma_\mathrm{const}=0.06^{+0.07}_{-0.05}$. A model with a steeper slope ($\alpha_\mathrm{grow}=2.39 \pm 0.06$) and a scatter that grows with decreasing $M_\mathrm{peak}$ is also consistent with the observed SSMF but is not required. Our new model for the satellite-subhalo connection, based on hundreds of Local Volume satellite galaxies, is in line with what was previously derived using only the Milky Way satellites.

astro-ph.GA↗

arXiv2022

ELVES III: Environmental Quenching by Milky Way-Mass Hosts

Isolated dwarf galaxies usually exhibit robust star formation but satellite dwarf galaxies are often devoid of young stars, even in Milky Way-mass groups. Dwarf galaxies thus offer an important laboratory of the environmental processes that cease star formation. We explore the balance of quiescent and star-forming galaxies (quenched fractions) for a sample of ~400 satellite galaxies around 30 Local Volume hosts from the Exploration of Local VolumE Satellites (ELVES) Survey. We present quenched fractions as a function of satellite stellar mass, projected radius, and host halo mass, to conclude that overall, the quenched fractions are similar to the Milky Way, dropping below 50% at satellite M* ~ 10^8 M_sun. We may see hints that quenching is less efficient at larger radius. Through comparison with the semi-analytic modeling code satgen, we are also able to infer average quenching times as a function of satellite mass in host halo-mass bins. There is a gradual increase in quenching time with satellite stellar mass rather than the abrupt change from rapid to slow quenching that has been inferred for the Milky Way. We also generally infer longer average quenching times than recent hydrodynamical simulations. Our results are consistent with models that suggest a wide range of quenching times are possible via ram-pressure stripping, depending on the clumpiness of the circumgalactic medium, the orbits of the satellites, and the degree of earlier preprocessing.

astro-ph.GA↗

arXiv2022

A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus

We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries likely have diameters greater than 1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. To date we have covered 624 square degrees of sky near to and interior to the orbit of Venus. The average images go to 21.3 mags in the r-band, with the best images near 22nd mag. Our new discovery 2021 PH27 has the smallest semi-major axis known for an asteroid, 0.4617 au, and the largest general relativistic effects (53 arcseconds/century) known for any body in the Solar System. The survey has detected about 15 percent of all known Atira NEOs. We put strong constraints on any stable population of Venus co-orbital resonance objects existing, as well as the Atira and Vatira asteroid classes. These interior asteroid populations are important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that cannot easily be discovered in other surveys. Comparing the actual population of asteroids found interior to Earth and Venus with those predicted to exist by extrapolating from the known population exterior to Earth is important to better understand the origin, composition and structure of the NEO population.

astro-ph.EP↗

arXiv2021

NGC5846-UDG1: A galaxy formed mostly by star formation in massive, extremely dense clumps of gas

It has been shown that ultra-diffuse galaxies (UDGs) have higher specific frequencies of globular clusters on average than other dwarf galaxies with similar luminosities. The UDG NGC5846-UDG1 is among the most extreme examples of globular cluster-rich galaxies found so far. Here we present new Hubble Space Telescope (HST) observations and analysis of this galaxy and its globular cluster system. We find that NGC5846-UDG1 hosts $54 \pm 9$ globular clusters, three to four times more than any previously known galaxy with a similar luminosity, and higher than reported in previous studies. With a galaxy luminosity of $L_{V,\mathrm{gal}} \approx 6 \times 10^7\,{\rm L}_{\odot}$ ($M_\star \approx 1.2 \times 10^8\,{\rm M}_\odot$) and a total globular cluster luminosity of $L_{V,\mathrm{GCs}} \approx 7.6 \times 10^6\,{\rm L}_{\odot}$, we find that the clusters currently comprise $\sim 13 \%$ of the total light. Taking into account the effects of mass loss from clusters during their formation and throughout their lifetime, we infer that most of the stars in the galaxy likely formed in globular clusters, and very little to no "normal" low-density star formation occurred. This result implies that the most extreme conditions during early galaxy formation promoted star formation in massive and dense clumps, in contrast to the dispersed star formation observed in galaxies today.

astro-ph.GA↗

arXiv2019

Using Surface Brightness Fluctuations to Study Nearby Satellite Galaxy Systems: Calibration and Methodology

We explore the use of ground-based surface brightness fluctuation (SBF) measurements to constrain distances to nearby dwarf galaxies. Using archival CFHT Megacam imaging data for a sample of 27 nearby dwarfs, we demonstrate that reliable SBF measurements and distances accurate to 15\% are possible even for very low surface brightness (LSB, $\mu_{i0}>24$ mag/arcsec$^2$) galaxies with modest, $\sim$hour-long exposures with CFHT. Combining our sample with a recent sample of 7 dwarfs with SBF measured with HST from the literature, we provide the most robust empirical SBF calibration to-date for the blue colors expected for these low mass systems. Our calibration is credible over the color range $0.3\lesssim g-i\lesssim0.8$ mag. It is also the first SBF calibration tied completely to TRGB distances as each galaxy in the sample has a literature TRGB distance. We find that even though the intrinsic scatter in SBF increases for blue galaxies, the rms scatter in the calibration is still $\lesssim0.3$ mag. We verify our measurements by comparing with HST SBF measurements and detailed image simulations. We argue that ground-based SBF is a very useful tool for characterizing dwarf satellite systems and field dwarfs in the nearby, D$\lesssim$20 Mpc universe.

astro-ph.GA↗

arXiv2019

Using Surface Brightness Fluctuations to Study Nearby Satellite Galaxy Systems: the Complete Satellite System of M101

We use surface brightness fluctuation (SBF) measurements to constrain the distance to low surface brightness (LSB) dwarfs in the vicinity of M101. Recent work has discovered many LSB candidate satellite companions of M101. However, without accurate distances, it is problematic to identify these dwarfs as physical satellites of M101. We use CFHT Legacy Survey (CFHTLS) data to measure the SBF signal for 43 candidate dwarfs. The data is deep enough that we constrain 29 of these to be unassociated background galaxies by their lack of SBF. We measure high S/N SBF signals for two of the candidate dwarfs, which are consistent with being at the distance of M101. The remaining candidates are too LSB and/or small for their distances to be constrained. Still, by comparison with Local Group dwarfs, we argue that the M101 satellite system is likely now complete down to stellar masses of $\sim5\times10^5$ M$_\odot$. We also provide a new SBF distance for the nearby dwarf UGC 8882, which suggests that it is significantly outside of the virial radius of M101 and is thus not a physical satellite. By constraining the distances to a majority of the candidates using only archival data, our work demonstrates the usefulness of SBF for nearby LSB galaxies and for studying the satellite systems of nearby massive galaxies.

astro-ph.GA↗