Searcharxiv⌕ Search

arXiv subjects

Christopher Martin

Publications and source records attributed to Christopher Martin.

34 records · Page 2Linked to original sources
arXiv2020

A "blue ring nebula" surrounding a thousands of years old stellar merger

Stellar mergers are a brief-lived but common phase in the evolution of binary star systems. Among the many astrophysical implications of these events include the creation of atypical stars (e.g. magnetic stars, blue stragglers, rapid rotators), interpretation of stellar populations, and formation channels of LIGO-detected compact object mergers. Although stellar mergers are thus commonly invoked phenomena, observations of these events and details of their evolution remain elusive. While a handful of stellar mergers have been directly observed in recent years, the central remnants of these events remain shrouded by an opaque shell of dust and molecules, making it impossible to observe their final state (e.g. as a single merged star or a tighter surviving binary). Here we report observations of an unusual, ring-shaped ultraviolet nebula and the star at its center, TYC 2597-735-1. The nebula shows two opposing fronts, suggesting a bipolar outflow from TYC 2597-735-1. TYC 2597-735-1's spectrum and proximity above the Galactic plane suggest it is an old star, yet it shows abnormally low surface gravity and a detectable long-term luminosity decay, uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits H-alpha emission, radial velocity variations, enhanced ultraviolet radiation, and excess infrared emission, common signposts of dusty circumstellar disks, stellar activity, and accretion. The combined observations, paired with stellar evolution models, suggests TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger found at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, directly inferring how two stars merge into a single star.

astro-ph.SR↗
arXiv2020

Similar Scaling Relations for the Gas Content of Galaxies across Environments to z ~ 3.5

We study the effects of the local environment on the molecular gas content of a large sample of log($M_{*}$/$M_{\odot}$) $\gtrsim$ 10 star-forming and starburst galaxies with specific star-formation rates (sSFRs) on and above the main sequence (MS) to $z$ $\sim$ 3.5. ALMA observations of the dust continuum in the COSMOS field are used to estimate molecular gas masses at $z$ $\approx$ 0.5-3.5. We also use a local universe sample from the ALFALFA HI survey after converting it into molecular masses. The molecular mass ($M_{ISM}$) scaling relation shows a dependence on $z$, $M_{*}$, and sSFR relative to the MS, but no dependence on environmental overdensity $Δ$ ($M_{ISM}$ $\propto$ $Δ^{0.03}$). Similarly, gas mass fraction (f$_{gas}$) and depletion timescale ($τ$) show no environmental dependence to $z$ $\sim$ 3.5. At $\langle z\rangle$ $\sim$ 1.8, the average $\langle M_{ISM}\rangle$,$\langle$f$_{gas}\rangle$, and $\langle τ\rangle$ in densest regions is (1.6$\pm$0.2)$\times$10$^{11}$ $M_{\odot}$, 55$\pm$2%, and 0.8$\pm$0.1 Gyr, respectively, similar to those in the lowest density bin. Independent of the environment, f$_{gas}$ decreases and $τ$ increases with increasing cosmic time. Cosmic molecular mass density ($ρ$) in the lowest density bins peaks at $z$ $\sim$ 1-2, and this peak happens at $z$ $<$ 1 in densest bins. This differential evolution of $ρ$ across environments is likely due to the growth of the large-scale structure with cosmic time. Our results suggest that the molecular gas content and the subsequent star-formation activity of log($M_{*}$/$M_{\odot}$) $\gtrsim$ 10 star-forming and starburst galaxies is primarily driven by internal processes, and not by their local environment since $z$ $\sim$ 3.5.

astro-ph.GA↗
arXiv2020

Spectroscopic Confirmation of a Coma Cluster Progenitor at z ~ 2.2

We report the spectroscopic confirmation of a new protocluster in the COSMOS field at $z$ $\sim$ 2.2, COSMOS Cluster 2.2 (CC2.2), originally identified as an overdensity of narrowband selected H$α$ emitting candidates. With only two masks of Keck/MOSFIRE near-IR spectroscopy in both $H$ ($\sim$ 1.47-1.81 $μ$m) and $K$ ($\sim$ 1.92-2.40 $μ$m) bands ($\sim$ 1.5 hour each), we confirm 35 unique protocluster members with at least two emission lines detected with S/N $>$ 3. Combined with 12 extra members from the zCOSMOS-deep spectroscopic survey (47 in total), we estimate a mean redshift and a line-of-sight velocity dispersion of $z_{mean}$=2.23224 $\pm$ 0.00101 and $σ_{los}$=645 $\pm$ 69 km s$^{-1}$ for this protocluster, respectively. Assuming virialization and spherical symmetry for the system, we estimate a total mass of $M_{vir}$ $\sim$ $(1-2) \times$10$^{14}$ $M_{\odot}$ for the structure. We evaluate a number density enhancement of $δ_{g}$ $\sim$ 7 for this system and we argue that the structure is likely not fully virialized at $z$ $\sim$ 2.2. However, in a spherical collapse model, $δ_{g}$ is expected to grow to a linear matter enhancement of $\sim$ 1.9 by $z$=0, exceeding the collapse threshold of 1.69, and leading to a fully collapsed and virialized Coma-type structure with a total mass of $M_{dyn}$($z$=0) $\sim$ 9.2$\times$10$^{14}$ $M_{\odot}$ by now. This observationally efficient confirmation suggests that large narrowband emission-line galaxy surveys, when combined with ancillary photometric data, can be used to effectively trace the large-scale structure and protoclusters at a time when they are mostly dominated by star-forming galaxies.

astro-ph.GA↗
arXiv2020

The FLASHES Survey I: Integral Field Spectroscopy of the CGM around 48 $z=2.3-3.1$ QSOs

We present the pilot study component of the Fluorescent Lyman-Alpha Structures in High-z Environments (FLASHES) Survey; the largest integral-field spectroscopy survey to date of the circumgalactic medium at $z=2.3-3.1$. We observed 48 quasar fields between 2015 and 2018 with the Palomar Cosmic Web Imager (Matuszewski et al. 2010). Extended HI Lyman-$\mathrmα$ emission is discovered around 42/48 of the observed quasars, ranging in projected, flux-weighted radius from 21-71 proper kiloparsecs (pkpc), with 26 nebulae exceeding $100\mathrm{~pkpc}$ in effective diameter. The circularly averaged surface brightness radial profile peaks at a maximum of $\mathrm{1\times 10^{-17}~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ ($2\times10^{-15}~\mathrm{erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ adjusted for cosmological dimming) and luminosities range from $1.9\times10^{43}~\mathrm{erg~s^{-1}}$ to $-14.1\times10^{43}~\mathrm{erg~s^{-1}}$. The emission appears to have a highly eccentric morphology and a maximum covering factor of $50\%$ ($60\%$ for giant nebulae). On average, the nebular spectra are red-shifted with respect to both the systemic redshift and Ly$α$ peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single or double-peaked line shapes with global dispersions ranging from $167~\mathrm{km~s^{-1}}$ to $690~\mathrm{km~s^{-1}}$, though the individual (Gaussian) components of lines with complex shapes mostly appear to have dispersions $\leq 400$ $\mathrm{km~s^{-1}}$, and the flux-weighted velocity centroids of the lines vary by thousands of $ \mathrm{km~s^{-1}}$ with respect to the systemic QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with gravitational motions expected in dark matter halos of mass $\mathrm{M_h \simeq10^{12.5} M_\odot}$. We compare these results to existing surveys at both higher and lower redshift.

astro-ph.GA↗
arXiv2019

The Dark Matter Distributions in Low-Mass Disk Galaxies. II. The Inner Density Profiles

Dark matter-only simulations predict that dark matter halos have steep, cuspy inner density profiles, while observations of dwarf galaxies find a range of inner slopes that are often much shallower. There is debate whether this discrepancy can be explained by baryonic feedback or if it may require modified dark matter models. In Paper 1 of this series, we obtained high-resolution integral field H$α$ observations for 26 dwarf galaxies with $M_*=10^{8.1}-10^{9.7}\textrm{M}_\odot$. We derived rotation curves from our observations, which we use here to construct mass models. We model the total mass distribution as the sum of a generalized Navarro-Frenk-White (NFW) dark matter halo and the stellar and gaseous components. Our analysis of the slope of the dark matter density profile focuses on the inner 300-800 pc, chosen based on the resolution of our data and the region resolved by modern hydrodynamical simulations. The inner slope measured using ionized and molecular gas tracers is consistent, and it is additionally robust to the choice of stellar mass-to-light ratio. We find a range of dark matter profiles, including both cored and cuspy slopes, with an average of $ρ_{\rm DM}\sim r^{-0.74\pm 0.07}$, shallower than the NFW profile, but steeper than those typically observed for lower-mass galaxies with $M_*\sim 10^{7.5}\textrm{M}_\odot$. Simulations that reproduce the observed slopes in those lower-mass galaxies also produce slopes that are too shallow for galaxies in our mass range. We therefore conclude that supernova feedback models do not yet provide a fully satisfactory explanation for the observed trend in dark matter slopes.

astro-ph.GA↗
arXiv2019

Spatially-resolved stellar kinematics of the ultra diffuse galaxy Dragonfly 44. I. Observations, kinematics, and cold dark matter halo fits

We present spatially-resolved stellar kinematics of the well-studied ultra diffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hrs of observations with the Keck Cosmic Web Imager. The luminosity-weighted dispersion within the half-light radius is $σ_{1/2}=33^{+3}_{-3}$ km/s. There is no evidence for rotation, with $V/σ<0.12$ (90% confidence) along the major axis, in apparent conflict with models where UDGs are the high-spin tail of the normal dwarf galaxy distribution. The spatially-averaged line profile is more peaked than a Gaussian, with Gauss-Hermite coefficient $h_4=0.13\pm 0.05$. The mass-to-light ratio within the effective radius is $M/L=26^{+7}_{-6}$, similar to other UDGs and higher by a factor of six than normal galaxies of the same luminosity. This difference between UDGs and other galaxies is, however, sensitive to the aperture that is used, and is much reduced when the $M/L$ ratios are measured within a fixed radius of 10 kpc. Dragonfly 44 has a rising velocity dispersion profile, from $σ=26^{+4}_{-4}$ km/s at R=0.2 kpc to $σ=41^{+8}_{-8}$ km/s at R=5.1 kpc. The profile can only be fit with a cuspy NFW profile if the orbital distribution has strong tangential anisotropy, with $β=-0.8^{+0.4}_{-0.5}$. An alternative explanation is that the dark matter profile has a core: a Di Cintio et al. (2014) density profile with a mass-dependent core provides a very good fit to the kinematics for a halo mass of $\log (M_{200}/{\rm M}_{\odot})=11.2^{+0.6}_{-0.6}$ and $β=-0.1^{+0.2}_{-0.3}$, i.e., isotropic orbits. This model predicts a slight positive kurtosis, in qualitative agreement with the measured $h_4$ parameter. UDGs such as Dragonfly 44 are dark matter dominated even in their centers, and can constrain the properties of dark matter in a regime where baryons usually dominate the kinematics: small spatial scales in massive halos.

astro-ph.GA↗
arXiv2019

Spatially Resolved Stellar Kinematics of the Ultra-Diffuse Galaxy Dragonfly 44: II. Constraints on Fuzzy Dark Matter

Given the absence of directly detected dark matter (DM) as weakly interacting massive particles, there is strong interest in the possibility that DM is an ultra-light scalar field, here denoted as fuzzy DM. Ultra-diffuse galaxies, with the sizes of giant galaxies and the luminosities of dwarf galaxies, have a wide range of DM halo masses, thus providing new opportunities for exploring the connections between galaxies and their DM halos. Following up on new integral field unit spectroscopic observations and dynamics modeling of the DM-dominated ultra-diffuse galaxy Dragonfly 44 in the outskirts of the Coma Cluster, we present models of fuzzy DM constrained by the stellar dynamics of this galaxy. We infer a scalar field mass of $\sim 3 \times 10^{-22}$ eV, consistent with other constraints from galaxy dynamics but in tension with constraints from Ly$α$ forest power spectrum modeling. While we are unable to statistically distinguish between fuzzy DM and normal cold DM models, we find that the inferred properties of the fuzzy DM halo satisfy a number of predictions for halos in a fuzzy DM cosmology. In particular, we find good agreement with the predicted core size--halo mass relation and the predicted transition radius between the quantum pressure-dominated inner region and the outer halo region.

astro-ph.GA↗
arXiv2019

The Dark Matter Distributions in Low-Mass Disk Galaxies. I. H$α$ Observations Using the Palomar Cosmic Web Imager

Dark-matter-only simulations predict that dark matter halos have cusp-like inner density profiles, while observations of low-mass galaxies have found a range of inner slopes that are typically much shallower. It is still not well established whether this discrepancy can be explained by baryonic feedback or if it may require modified dark matter models. To better understand the diversity of dark matter profiles in dwarf galaxies, we undertook a survey of 26 low-mass galaxies ($\log M_*/\textrm{M}_\odot = 8.4-9.8$, $v_{\rm max} = 50-140$ km s$^{-1}$) within 30 Mpc using the Palomar Cosmic Web Imager, which is among the largest integral field spectroscopic surveys of its type. In this paper, we derive H$α$ velocity fields for the full sample with a typical spatial resolution of $\sim$160 pc. We extract rotation curves and verify their robustness to several choices in the analysis. We present a method for improving the velocity precision obtained from image slicing spectrographs using narrowband H$α$ images. For 11 galaxies, we compare the H$α$ velocity fields to CO kinematics measured using CARMA, finding the maps to be in good agreement. The standard deviation of the difference is typically $\sim$7 km s$^{-1}$, comparable to the level of turbulence in the interstellar medium, showing that the two tracers have substantially the same bulk kinematics. In a companion paper, we will use the rotation curves produced here to construct mass models of the galaxies and determine their dark matter density profiles.

astro-ph.GA↗
arXiv2018

Keck/Palomar Cosmic Web Imagers (KCWI/PCWI) Reveal an Enormous Ly$α$ Nebula in an Extremely Overdense QSO Pair Field at $z=2.45$

Enormous Ly$α$ nebulae (ELANe) represent the extrema of Ly$α$ nebulosities. They have detected extents of $>200$ kpc in Ly$α$ and Ly$α$ luminosities $>10^{44}$ erg s$^{-1}$. The ELAN population is an ideal laboratory to study the interactions between galaxies and the intergalactic/circumgalactic medium (IGM/CGM) given their brightness and sizes. The current sample size of ELANe is still very small, and the few $z\approx2$ ELANe discovered to date are all associated with local overdensities of active galactic nuclei (AGNs). Inspired by these results, we have initiated a survey of ELANe associated with QSO pairs using the Palomar and Keck Cosmic Web Imagers (PCWI/KCWI). In this letter, we present our first result: the discovery of ELAN0101+0201 associated with a QSO pair at $z=2.45$. Our PCWI discovery data shows that, above a 2-$σ$ surface brightness of $1.2\times10^{-17}$ \sbunit, the end-to-end size of ELAN0101+0201 is $\gtrsim 232$ kpc. We have conducted follow-up observations using KCWI, resolving multiple Ly$α$ emitting sources within the rectangular field-of-view of $\approx 130\times165$ projected kpc$^2$, and obtaining their emission line profiles at high signal-to-noise ratios. Combining both KCWI and PCWI, our observations confirm that ELAN0101+0201 resides in an extremely overdense environment. Our observations further support that a large amount of cool ($T\sim10^4$K) gas could exist in massive halos (M$\gtrsim10^{13}$M$_\odot$) at $z\approx2$. Future observations on a larger sample of similar systems will provide statistics of how cool gas is distributed in massive overdensities at high-redshift and strongly constrain the evolution of the intracluster medium (ICM).

astro-ph.GA↗
arXiv2018

Quenching or Bursting: the Role of Stellar Mass, Environment, and Specific Star Formation Rate to $z$ $\sim$ 1

Using a novel approach, we study the quenching and bursting of galaxies as a function of stellar mass ($M_{*}$), local environment ($Σ$), and specific star-formation rate (sSFR) using a large spectroscopic sample of $\sim$ 123,000 $GALEX$/SDSS and $\sim$ 420 $GALEX$/COSMOS/LEGA-C galaxies to $z$ $\sim$ 1. We show that out to $z$ $\sim$ 1 and at fixed sSFR and local density, on average, less massive galaxies are quenching, whereas more massive systems are bursting, with a quenching/bursting transition at log($M_{*}$/$M_{\odot}$) $\sim$ 10.5-11 and likely a short quenching/bursting timescale ($\lesssim$ 300 Myr). We find that much of the bursting of star-formation happens in massive (log($M_{*}$/$M_{\odot}$) $\gtrsim$ 11), high sSFR galaxies (log(sSFR/Gyr$^{-1}$) $\gtrsim$ -2), particularly those in the field (log($Σ$/Mpc$^{-2}$) $\lesssim$ 0; and among group galaxies, satellites more than centrals). Most of the quenching of star-formation happens in low-mass (log($M_{*}$/$M_{\odot}$) $\lesssim$ 9), low sSFR galaxies (log(sSFR/Gyr$^{-1}$) $\lesssim$ -2), in particular those located in dense environments (log($Σ$/Mpc$^{-2}$) $\gtrsim$ 1), indicating the combined effects of $M_{*}$ and $Σ$ in quenching/bursting of galaxies since $z$ $\sim$ 1. However, we find that stellar mass has stronger effects than environment on recent quenching/bursting of galaxies to $z$ $\sim$ 1. At any given $M_{*}$, sSFR, and environment, centrals are quenchier (quenching faster) than satellites in an average sense. We also find evidence for the strength of mass and environmental quenching being stronger at higher redshift. Our preliminary results have potential implications for the physics of quenching/bursting in galaxies across cosmic time.

astro-ph.GA↗
arXiv2012

Halo Occupation Distribution Modeling of Green Valley Galaxies

We present a clustering analysis of near ultraviolet (NUV) - optical color selected luminosity bin samples of green valley galaxies. These galaxy samples are constructed by matching the Sloan Digital Sky Survey Data Release 7 with the latest Galaxy Evolution Explorer source catalog which provides NUV photometry. We present cross-correlation function measurements and determine the halo occupation distribution of these transitional galaxies using a new multiple tracer analysis technique. We extend the halo-occupation formalism to model the cross-correlation function between a galaxy sample of interest and multiple tracer populations simultaneously. This method can be applied to commonly used luminosity threshold samples as well as to color and luminosity bin selected galaxy samples, and improves the accuracy of clustering analyses for sparse galaxy populations. We confirm the previously observed trend that red galaxies reside in more massive halos and are more likely to be satellite galaxies than average galaxies of similar luminosity. While the change in central galaxy host mass as a function of color is only weakly constrained, the satellite fraction and characteristic halo masses of green satellite galaxies are found to be intermediate between those of blue and red satellite galaxies.

astro-ph.CO↗
arXiv2010

Catalogs of Hot White Dwarfs in the Milky Way from GALEX's Ultraviolet Sky Surveys. Constraining Stellar Evolution

We present comprehensive catalogs of hot star candidates in the Milky Way, selected from GALEX far-UV (FUV, 1344-1786 AA) and near-UV (NUV, 1771-2831 AA) imaging. The FUV and NUV photometry allows us to extract the hottest stellar objects, in particular hot white dwarfs (WD), which are elusive at other wavelengths because of their high temperatures and faint optical luminosities. We generated catalogs of UV sources from two GALEX's surveys: AIS (All-Sky Imaging Survey, depth ABmag~19.9/20.8 in FUV/NUV) and MIS (Medium-depth Imaging Survey, depth ~22.6/22.7mag). The two catalogs (from GALEX fifth data release) contain 65.3/12.6 million (AIS/MIS) unique UV sources with error(NUV)<0.5mag, over 21,435/1,579 square degrees. We also constructed subcatalogs of the UV sources with matched optical photometry from SDSS (7th data release): these contain 0.6/0.9million (AIS/MIS) sources with errors <0.3mag in both FUV and NUV, excluding sources with multiple optical counterparts, over an area of 7,325/1,103 square degrees. All catalogs are available online. We then selected 28,319(AIS)/9,028(MIS) matched sources with FUV-NUV<-0.13; this color cut corresponds to stellar Teff hotter than ~18,000 K. An additional color cut of NUV-r>0.1 isolates binaries with largely differing Teff's, and some intruding QSOs. Available spectroscopy for a subsample indicates that hot-star candidates with NUV-r<0.1 have negligible contamination by non-stellar objects. We discuss the distribution of sources in the catalogs, and the effects of error and color cuts on the samples. The density of hot-star candidates increases from high to low Galactic latitudes, but drops on the MW plane due to dust extinction. Our hot-star counts at all latitudes are better matched by Milky Way models computed with an initial-final mass relation that favours lower final masses. (ABRIDGED)

astro-ph.SR↗
arXiv2009

A Vigorous Explorer Program

Explorers have made breakthroughs in many fields of astrophysics. The science from both these missions contributed to three Nobel Prizes - Giacconi (2002), Mather, and Smoot (2006). Explorers have: marked the definitive beginning of precision cosmology, discovered that short gamma-ray bursts are caused by compact star mergers and have measured metalicity to redshifts z>6. NASA Explorers do cutting-edge science that cannot be done by facility-class instruments. The Explorer program provides a rapid response to changing science and technology, to enable cutting-edge science at moderate cost. Explorers also enable innovation, and engage & train scientists, managers and engineers, adding human capital to NASA and the nation. The astrophysics Explorer launch rate now being achieved is 1 per 3 years, and budget projections are in the $150M/year range for the next five years. A newly Vigorous Explorer Program should be created to: 1. Reach the long-stated goal of annual astrophysics launches; 2. Find additional launch options for Explorers and actively encourage cost savings in launchers and spacecraft, such as new commercial vehicles and innovative partnerships. 3. Mitigate risk via stronger technical development and sub-orbital programs, and through longer, more thorough, Phase A programs, potentially reducing the need for a 30% contingency; 4. Strive to protect the funding for missions that have reached Phase B, to prevent significant launch slips and cancellations, with a goal of 4 to 5 years from Phase B to launch; 5. Review the project management procedures and requirements to seek cost reductions, including the risk management strategy and the review and reporting process; 6. Review and possibly modify the cost caps for all Explorer classes to optimize scientific returns per dollar. [ABRIDGED]

astro-ph.IM↗
arXiv2005

Spitzer view on the evolution of star-forming galaxies from z=0 to z~3

We use a 24 micron selected sample containing more than 8,000 sources to study the evolution of star-forming galaxies in the redshift range from z=0 to z~3. We obtain photometric redshifts for most of the sources in our survey using a method based on empirically-built templates spanning from ultraviolet to mid-infrared wavelengths. The accuracy of these redshifts is better than 10% for 80% of the sample. The derived redshift distribution of the sources detected by our survey peaks at around z=0.6-1.0 (the location of the peak being affected by cosmic variance), and decays monotonically from z~1 to z~3. We have fitted infrared luminosity functions in several redshift bins in the range 0 1.e11 L_sun) to the total SFR density increases steadily from z~0 up to z~2.5, forming at least half of the newly-born stars by z~1.5. Ultraluminous infrared galaxies (L_TIR>1.e12 L_sun) play a rapidly increasing role for z>~1.3.

astro-ph↗
arXiv2004

The Properties of Ultraviolet-Luminous Galaxies at the Current Epoch

We have used the first matched set of GALEX and SDSS data to investigate the properties of a sample of 74 nearby galaxies with far-ultraviolet luminosities chosen to overlap the luminosity range of typical high-z Lyman Break Galaxies (LBGs). GALEX deep surveys have shown that ultraviolet-luminous galaxies (UVLGs) similar to these are the fastest evolving component of the UV galaxy population. Model fits to the combined GALEX and SDSS photometry yield typical FUV extinctions similar to LBGs. The implied star formation rates are SFR ~ 3 to 30 solar mass per year. This overlaps the range of SFRs for LBGs. We find a strong inverse correlation between galaxy mass and far-ultraviolet surface brightness, and on this basis divide the sample into ``large'' and ``compact'' UVLGs. The compact UVLGs have half-light radii of a few kpc or less (similar to LBGs). They are relatively low mass galaxies (~10 billion solar masses) with typical velocity dispersions of 60 to 150 km/s. They span a range in metallicity from 0.3 to 1 times solar, have blue optical-UV colors, and are forming stars at a rate sufficient to build the present galaxy in ~a Gigayear. In all these respects they appear similar to the LBG population. These ``living fossils'' may therefore provide an opportunity for detailed investigation of the physical processes occurring in typical star forming galaxies in the early universe.

astro-ph↗
arXiv2004

Millimeter and Submillimeter Survey of the R Corona Australis Region

Using a combination of data from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), the Arizona Radio Observatory Kitt Peak 12m telescope and the Arizona Radio Observatory 10m Heinrich Hertz Telescope, we have studied the most active part of the R CrA molecular cloud in multiple transitions of Carbon Monoxide, HCO$^+$ and 870\micron continuum emission. Since R CrA is nearby (130 pc), we are able to obtain physical spatial resolution as high as 0.01pc over an area of 0.16 pc$^2$, with velocity resolution finer than 1 km/s. Mass estimates of the protostar driving the mm-wave emission derived from HCO$^+$, dust continuum emission and kinematic techniques point to a young, deeply embedded protostar of $\sim$0.5-0.75 M$_\odot$, with a gaseous envelope of similar mass. A molecular outflow is driven by this source that also contains at least 0.8 M$_\odot$ of molecular gas with $\sim$0.5 L$_\odot$ of mechanical luminosity. HCO$^+$ lines show the kinematic signature of infall motions as well as bulk rotation. The source is most likely a Class 0 protostellar object not yet visible at near-IR wavelengths. With the combination of spatial and spectral resolution in our data set, we are able to disentangle the effects of infall, rotation and outflow towards this young object.

astro-ph↗