arXiv subjects

Steven Janowiecki

Publications and source records attributed to Steven Janowiecki.

At least 55 records · Page 3Linked to original sources

arXiv2017

xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies

We introduce xCOLD GASS, a legacy survey providing a census of molecular gas in the local Universe. Building upon the original COLD GASS survey, we present here the full sample of 532 galaxies with CO(1-0) measurements from the IRAM-30m telescope. The sample is mass-selected in the redshift interval $0.01 10^9$M$_{\odot}$. The CO(1-0) flux measurements are complemented by observations of the CO(2-1) line with both the IRAM-30m and APEX telescopes, HI observations from Arecibo, and photometry from SDSS, WISE and GALEX. Combining the IRAM and APEX data, we find that the CO(2-1) to CO(1-0) luminosity ratio for integrated measurements is $r_{21}=0.79\pm0.03$, with no systematic variations across the sample. The CO(1-0) luminosity function is constructed and best fit with a Schechter function with parameters {$L_{\mathrm{CO}}^* = (7.77\pm2.11) \times 10^9\,\mathrm{K\,km\,s^{-1}\, pc^{2}}$, $ϕ^{*} = (9.84\pm5.41) \times 10^{-4} \, \mathrm{Mpc^{-3}}$ and $α= -1.19\pm0.05$}. With the sample now complete down to stellar masses of $10^9$M$_{\odot}$, we are able to extend our study of gas scaling relations and confirm that both molecular gas fraction and depletion timescale vary with specific star formation rate (or offset from the star-formation main sequence) much more strongly than they depend on stellar mass. Comparing the xCOLD GASS results with outputs from hydrodynamic and semi-analytic models, we highlight the constraining power of cold gas scaling relations on models of galaxy formation.

astro-ph.GA↗

arXiv2017

(Almost) Dark Galaxies in the ALFALFA Survey: Isolated HI Bearing Ultra Diffuse Galaxies

We present a sample of 115 very low optical surface brightness, highly extended, HI-rich galaxies carefully selected from the ALFALFA survey that have similar optical absolute magnitudes, surface brightnesses, and radii to recently discovered "ultra-diffuse" galaxies (UDGs). However, these systems are bluer and have more irregular morphologies than other UDGs, are isolated, and contain significant reservoirs of HI. We find that while these sources have normal star formation rates for HI selected galaxies of similar stellar mass, they have very low star formation efficiencies. We further present deep optical and HI synthesis follow up imaging of three of these HI-bearing ultra-diffuse sources. We measure HI diameters extending to ~40 kpc, but note that while all three sources have large HI diameters for their stellar mass, they are consistent with the HI mass - HI radius relation. We further analyze the HI velocity widths and rotation velocities for the unresolved and resolved sources respectively, and find that the sources appear to inhabit halos of dwarf galaxies. We estimate spin parameters, and suggest that these sources may exist in high spin parameter halos, and as such may be potential HI-rich progenitors to the ultra-diffuse galaxies observed in cluster environments.

astro-ph.GA↗

arXiv2017

Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525

We report on the detection at $>$98% confidence of an optical counterpart to AGC 249525, an Ultra-Compact High Velocity Cloud (UCHVC) discovered by the ALFALFA blind neutral hydrogen survey. UCHVCs are compact, isolated HI clouds with properties consistent with their being nearby low-mass galaxies, but without identified counterparts in extant optical surveys. Analysis of the resolved stellar sources in deep $g$- and $i$-band imaging from the WIYN pODI camera reveals a clustering of possible Red Giant Branch stars associated with AGC 249525 at a distance of 1.64$\pm$0.45 Mpc. Matching our optical detection with the HI synthesis map of AGC 249525 from Adams et al. (2016) shows that the stellar overdensity is exactly coincident with the highest-density HI contour from that study. Combining our optical photometry and the HI properties of this object yields an absolute magnitude of $-7.1 \leq M_V \leq -4.5$, a stellar mass between $2.2\pm0.6\times10^4 M_{\odot}$ and $3.6\pm1.0\times10^5 M_{\odot}$, and an HI to stellar mass ratio between 9 and 144. This object has stellar properties within the observed range of gas-poor Ultra-Faint Dwarfs in the Local Group, but is gas-dominated.

astro-ph.GA↗

arXiv2017

Structural and Photometric Properties of the Andromeda Satellite Dwarf Galaxy Lacerta I from Deep Imaging with WIYN pODI

We present results from WIYN pODI imaging of Lacerta I (And XXXI), a satellite dwarf galaxy discovered in the outskirts of the Andromeda galaxy (M31) in Pan-STARRS1 survey data. Our deep, wide-field $g,i$ photometry reaches $\sim$3 magnitudes fainter than the photometry in the Pan-STARRS1 discovery paper and allows us to trace the stellar population of Lac I beyond two half-light radii from the galaxy center. We measure a Tip of the Red Giant Branch (TRGB) distance for Lac I of $(m-M)_0=24.44\pm0.11$ mag (773$\pm$40 kpc, or 264$\pm$6 kpc from M31), which is consistent with the Pan-STARRS1 distance. We use a maximum-likelihood technique to derive structural properties for the galaxy, and find a half-light radius ($r_h$) of 3.24$\pm$0.21 arcmin (728$\pm$47 pc), ellipticity ($ε$) of 0.44$\pm$0.03, total magnitude $M_V$ $=$ $-$11.4$\pm$0.3, and central surface brightness $μ_{V,0}$ $=$ 24.8$\pm$0.3 mag arcsec$^{-2}$. We find no HI emission in archival data and set a limit on Lac I's neutral gas mass-to-light ratio of $M_{HI}/L_V$ $<$ 0.06 $M_{sun}$/$L_{sun}$, confirming Lac I as a gas-poor dwarf spheroidal galaxy. Photometric metallicities derived from Red Giant Branch stars within 2 $r_h$ yield a median [Fe/H] of $-$1.68$\pm$0.03, which is more metal-rich than the spectroscopically-derived value from Martin et al. (2014). Combining our measured magnitude with this higher metallicity estimate places Lac I closer to its expected position on the luminosity-metallicity relation for dwarf galaxies.

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arXiv2017

xGASS: Gas-rich central galaxies in small groups and their connections to cosmic web gas feeding

We use deep HI observations obtained as part of the extended GALEX Arecibo SDSS survey (xGASS) to study the cold gas properties of central galaxies across environments. We find that, below stellar masses of 10^10.2 Msun, central galaxies in groups have an average atomic hydrogen gas fraction ~0.3dex higher than those in isolation at the same stellar mass. At these stellar masses, group central galaxies are usually found in small groups of N=2 members. The higher HI content in these low mass group central galaxies is mirrored by their higher average star formation activity and molecular hydrogen content. At larger stellar masses, this difference disappears and central galaxies in groups have similar (or even smaller) gas reservoirs and star formation activity compared to those in isolation. We discuss possible scenarios able to explain our findings and suggest that the higher gas content in low mass group central galaxies is likely due to contributions from the cosmic web or HI-rich minor mergers, which also fuel their enhanced star formation activity.

astro-ph.GA↗

arXiv2016

The Burrell Schmidt Deep Virgo Survey: Tidal Debris, Galaxy Halos, and Diffuse Intracluster Light in the Virgo Cluster

We present a deep imaging survey of the Virgo Cluster, designed to study the connection between cluster galaxies and Virgo's diffuse intracluster light (ICL). Our observations span roughly 16 square degrees and reach a 3-sigma depth of mu(B)=29.5 and mu(V)=28.5 mag/arcsec^2. At these depths, the limiting systematic uncertainties are astrophysical: scattered starlight from foreground Galactic dust, and variations in faint background sources. The dust-scattered starlight is well-traced by deep far-infrared imaging, making it distinguishable from true Virgo diffuse light. Our imaging maps the Virgo core around M87 and the adjacent M86/M84 region, in subcluster B around M49, and in the more distant W' cloud around NGC 4365. Most of the detected ICL is found in the Virgo core and within the W' cloud, with little evidence for extensive ICL in subcluster B. The large amount of diffuse light seen in the infalling W' cloud likely illustrates the importance of the group environment for generating ICL. The bulk of the detected ICL is fairly red (B-V=0.7-0.9), indicative of old stellar populations. We estimate a total Virgo ICL fraction of 7-15%, somewhat smaller than expected for massive, evolved clusters, suggesting that Virgo is still growing its ICL component. We trace M87's extremely boxy halo out to ~ 150 kpc, and show that the current stripping rate of low luminosity galaxies is insufficient to have built M87's outer halo over a Hubble time. Finally, we identify another large ultra-diffuse galaxy in Virgo, likely in the process of being shredded by the cluster tidal field.

astro-ph.GA↗

arXiv2016

Constraining the Stellar Populations and Star Formation Histories of Blue Compact Dwarf Galaxies with SED Fits

We discuss and test possible evolutionary connections between Blue Compact Dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal laboratories to study intense star formation episodes in low mass dwarf galaxies, and have sometimes been considered a short-lived evolutionary stage between types of dwarf galaxies. To test these connections, we consider a sample of BCDs as well as a comparison sample of nearby galaxies from the Local Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy with a grid of theoretical models to determine their stellar masses and star formation properties. We compare our results for BCDs with the LVL galaxies to put BCDs in the context of normal galaxy evolution. The SED fits demonstrate that the star formation events currently underway in BCDs are at the extreme of the continuum of normal dwarf galaxies, both in terms of the relative mass involved and in the relative increase over previous star formation rates. Today's BCDs are distinctive objects in a state of extreme star formation which is rapidly transforming them. This study also suggests ways to identify former BCDs whose star formation episodes have since faded.

astro-ph.GA↗

arXiv2016

GALEX-SDSS-WISE Legacy Catalog (GSWLC): Star Formation Rates, Stellar Masses and Dust Attenuations of 700,000 Low-redshift Galaxies

In this paper, we present GALEX-SDSS-WISE Legacy Catalog (GSWLC), a catalog of physical properties (stellar masses, dust attenuations and star formation rates (SFRs)) of ~700,000 galaxies with SDSS redshifts below 0.3. GSWLC contains galaxies within the GALEX footprint, regardless of a UV detection, covering 90% of SDSS. The physical properties were obtained from UV/optical SED fitting following Bayesian methodology of Salim et al. (2007), with improvements such as blending corrections for low-resolution UV photometry, flexible dust attenuation laws, and emission line corrections. GSWLC includes mid-IR SFRs derived from IR templates based upon 22 micron WISE observations. These estimates are independent of UV/optical SED fitting, in order to separate possible systematics. The paper argues that the comparison of specific SFRs (SSFRs) is more informative and physically motivated than the comparison of SFRs. SSFRs resulting from the UV/optical SED fitting are compared to the mid-IR SSFRs, and to SSFRs from three published catalogs. For "main sequence" galaxies with no AGN contribution all SSFRs are in very good agreement (within 0.1 dex on average). In particular, the widely-used aperture-corrected SFRs from MPA/JHU catalog show no systematic offsets, in contrast to some integral-field spectroscopy results. For galaxies below the main sequence (log SSFR<-11), mid-IR (S)SFRs based on fixed luminosity-SFR conversion are severely biased (up to 2 dex) because the dust is primarily heated by old stars. Furthermore, mid-IR (S)SFRs are overestimated by up to 0.6 dex for galaxies with AGN, presumably due to non-stellar dust heating. UV/optical (S)SFRs are thus preferred to IR-based (S)SFRs for quenched galaxies and those which host AGN.

astro-ph.GA↗

arXiv2016

SHIELD: Comparing Gas and Star Formation in Low Mass Galaxies

We analyze the relationships between atomic, neutral hydrogen (HI) and star formation (SF) in the 12 low-mass SHIELD galaxies. We compare high spectral (~0.82 km/s/channel) and spatial resolution (physical resolutions of 170 pc - 700 pc) HI imaging from the VLA with Hαand far-ultraviolet imaging. We quantify the degree of co-spatiality between star forming regions and regions of high HI column densities. We calculate the global star formation efficiencies (SFE, $Σ_{\rm SFR}$ / $Σ_{\rm HI}$), and examine the relationships among the SFE and HI mass, HI column density, and star formation rate (SFR). The systems are consuming their cold neutral gas on timescales of order a few Gyr. While we derive an index for the Kennicutt-Schmidt relation of N ~ 0.68 $\pm$ 0.04 for the SHIELD sample as a whole, the values of N vary considerably from system to system. By supplementing SHIELD results with those from other surveys, we find that HI mass and UV-based SFR are strongly correlated over five orders of magnitude. Identification of patterns within the SHIELD sample allows us to bin the galaxies into three general categories: 1) mainly co-spatial HI and SF regions, found in systems with highest peak HI column densities and highest total HI masses, 2) moderately correlated HI and SF regions, found in systems with moderate HI column densities, and 3) obvious offsets between HI and SF peaks, found in systems with the lowest total HI masses. SF in these galaxies is dominated by stochasticity and random fluctuations in their ISM.

astro-ph.GA↗

arXiv2016

SHIELD: Neutral Gas Kinematics and Dynamics

We present kinematic analyses of the 12 galaxies in the "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD). We use multi-configuration interferometric observations of the HI 21cm emission line from the Karl G. Jansky Very Large Array (VLA) to produce image cubes at a variety of spatial and spectral resolutions. Both two- and three-dimensional fitting techniques are employed in an attempt to derive inclination-corrected rotation curves for each galaxy. In most cases, the comparable magnitudes of velocity dispersion and projected rotation result in degeneracies that prohibit unambiguous circular velocity solutions. We thus make spatially resolved position-velocity cuts, corrected for inclination using the stellar components, to estimate the circular rotation velocities. We find circular velocities <30 km/s for the entire survey population. Baryonic masses are calculated using single-dish HI fluxes from Arecibo and stellar masses derived from HST and Spitzer imaging. Comparison is made with total dynamical masses estimated from the position-velocity analysis. The SHIELD galaxies are then placed on the baryonic Tully-Fisher relation. There exists an empirical threshold rotational velocity <15 km/s, below which current observations cannot differentiate coherent rotation from pressure support. The SHIELD galaxies are representative of an important population of galaxies whose properties cannot be described by current models of rotationally-dominated galaxy dynamics.

astro-ph.GA↗

arXiv2016

ALFALFA Discovery of the Most Metal-Poor Gas-Rich Galaxy Known: AGC 198691

We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength study of galaxies with HI masses in the range of 10$^{6}$-10$^{7.2}$~M$_{\odot}$ discovered by the ALFALFA survey. We have obtained spectra of the lone HII region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the temperature-sensitive [OIII]$λ$4363 line and hence the determination of a "direct" oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 $\pm$ 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind HI survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.

astro-ph.GA↗

arXiv2015

Searching for Optical Counterparts to Ultra-compact High Velocity Clouds: Possible Detection of a Counterpart to AGC 198606

We report on initial results from a campaign to obtain optical imaging of a sample of Ultra Compact High Velocity Clouds (UCHVCs) discovered by the ALFALFA neutral hydrogen (HI) survey. UCHVCs are sources with velocities and sizes consistent with their being low-mass dwarf galaxies in the Local Volume, but without optical counterparts in existing catalogs. We are using the WIYN 3.5-m telescope and pODI camera to image these objects and search for an associated stellar population. In this paper, we present our observational strategy and method for searching for resolved stellar counterparts to the UCHVCs. We combine careful photometric measurements, a color-magnitude filter, and spatial smoothing techniques to search for stellar overdensities in the g- and i-band images. We also run statistical tests to quantify the likelihood that whatever overdensities we find are real and not chance superpositions of sources. We demonstrate the method by applying it to two data sets: WIYN imaging of Leo P, a UCHVC discovered by ALFALFA and subsequently shown to be a low-mass star-forming dwarf galaxy in the Local Volume, and WIYN imaging of AGC198606, an HI cloud identified by ALFALFA that is near in position and velocity to the Local Group dwarf Leo T. Applying the search method to the Leo P data yields an unambiguous detection (>99% confidence) of the galaxy's stellar population. Applying our method to the AGC198606 imaging yields a possible detection (92% confidence) of an optical counterpart located ~2.5 arc minutes away from the centroid of AGC198606's HI distribution and within the HI disk. We use the optical data to estimate a distance to the stellar counterpart between 373 and 393 kpc, with an absolute magnitude M_i = -4.67+/-0.09. Combining the WIYN data with our previous estimate of the HI mass of AGC198606 from WSRT imaging yields an HI-to-stellar mass ratio of ~45-110.

astro-ph.GA↗

arXiv2015

(Almost) Dark HI Sources in the ALFALFA Survey: The Intriguing Case of HI1232+20

We report the discovery and follow-up observations of a system of three objects identified by the ALFALFA extragalactic HI survey, cataloged as (almost) dark extragalactic sources, i.e., extragalactic HI detections with no discernible counterpart in publicly available, wide-field, imaging surveys. We have obtained deep optical imaging with WIYN pODI and HI synthesis maps with WSRT of the HI1232+20 system. The source with the highest HI flux has a newly discovered ultra-low surface brightness (LSB) optical counterpart associated with it, while the other two sources have no detected optical counterparts in our images. Our optical observations show that the detected LSB optical counterpart has a peak surface brightness of ~26.4 mag/arcsec^2 in g', which is exceptionally faint. This source (AGC 229385) has the largest accurately measured HI mass-to-light ratio of an isolated object: MHI/Lg'=46 Msun/Lsun, and has an HI mass of 7.2*10^8 Msun. The other two HI sources (with HI masses 2.0*10^8 and 1.2*10^8 Msun) without optical counterparts have upper limit surface brightnesses of 27.9 and 27.8 mag/arcsec^2 in g', and lower limits on their gas mass-to-light ratio of MHI/Lg'>57 and >31 Msun/Lsun. This system lies relatively close in projection to the Virgo Cluster, but velocity flow models indicate that it is located at ~25 Mpc, substantially beyond Virgo. The system appears to be quite isolated, with no known object closer than 500 kpc. These HI sources may represent both sides of the threshold between "dark" star-less galaxies and galaxies with stellar populations. We discuss a variety of possible formation scenarios for the HI1232+20 system.

astro-ph.GA↗

arXiv2014

The ALFALFA "Almost Darks" Campaign: Pilot VLA HI Observations of Five High Mass-to-Light Ratio Systems

We present VLA HI spectral line imaging of 5 sources discovered by ALFALFA. These targets are drawn from a larger sample of systems that were not uniquely identified with optical counterparts during ALFALFA processing, and as such have unusually high HI mass to light ratios. These candidate "Almost Dark" objects fall into 4 categories: 1) objects with nearby HI neighbors that are likely of tidal origin; 2) objects that appear to be part of a system of multiple HI sources, but which may not be tidal in origin; 3) objects isolated from nearby ALFALFA HI detections, but located near a gas-poor early-type galaxy; 4) apparently isolated sources, with no object of coincident redshift within ~400 kpc. Roughly 75% of the 200 objects without identified counterparts in the $α$.40 database (Haynes et al. 2011) fall into category 1. This pilot sample contains the first five sources observed as part of a larger effort to characterize HI sources with no readily identifiable optical counterpart at single dish resolution. These objects span a range of HI mass [7.41 < log(M$_{\rm HI}$) < 9.51] and HI mass to B-band luminosity ratios (3 < M$_{\rm HI}$/L$_{\rm B}$ < 9). We compare the HI total intensity and velocity fields to SDSS optical imaging and to archival GALEX UV imaging. Four of the sources with uncertain or no optical counterpart in the ALFALFA data are identified with low surface brightness optical counterparts in SDSS imaging when compared with VLA HI intensity maps, and appear to be galaxies with clear signs of ordered rotation. One source (AGC 208602) is likely tidal in nature. We find no "dark galaxies" in this limited sample. The present observations reveal complex sources with suppressed star formation, highlighting both the observational difficulties and the necessity of synthesis follow-up observations to understand these extreme objects. (abridged)

astro-ph.GA↗

arXiv2014

The Unique Structural Parameters of the Underlying Host Galaxies in Blue Compact Dwarfs

The nature of possible evolutionary pathways between various types of dwarf galaxies is still not fully understood. Blue compact dwarf galaxies (BCDs) provide a unique window into dwarf galaxy formation and evolution and are often thought of as an evolutionary stage between different classes of dwarf galaxies. In this study we use deep optical and near-infrared observations of the underlying hosts of BCDs in order to study the structural differences between different types of dwarf galaxies. When compared with dwarf irregular galaxies of similar luminosities, we find that the underlying hosts of BCDs have significantly more concentrated light distributions, with smaller scale lengths and brighter central surface brightnesses. We demonstrate here that the underlying hosts of BCDs are distinct from the broad continuum of typical dwarf irregular galaxies, and that it is unlikely that most dwarf irregular galaxies can transform into a BCD or vice versa. Furthermore, we find that the starburst in a BCD only brightens it on average by ~0.8 mag (factor of two), in agreement with other studies. It appears that a BCD is a long-lived and distinct type of dwarf galaxy that exhibits an exceptionally concentrated matter distribution. We suggest that it is this compact mass distribution that enables the strong star formation events that characterize this class of dwarf galaxy, that the compactness of the underlying host can be used as a distinguishing parameter between BCDs and other dwarf galaxies, and that it can also be used to identify BCDs which are not currently experiencing an intense starburst event.

astro-ph.GA↗

arXiv2014

Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68

We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% Z$_{\odot}$, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M$_{\rm HI}$ $=$ 2.8$\times$10$^{7}$ M$_{\odot}$), recently star-forming (SFR$_{\rm FUV}$ $=$ 1.4$\times$10$^{-3}$ M$_{\odot}$ yr$^{-1}$, SFR$_{\rm Hα}$ $<$ 7$\times$10$^{-5}$ M$_{\odot}$ yr$^{-1}$) companion has the same systemic velocity as DDO 68 (V$_{\rm sys}$ $=$ 506 km s$^{-1}$; D $=$ 12.74$\pm$0.27 Mpc) and is located at a projected distance of 42 kpc. New HI maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness HI gas forms a bridge between these objects.

astro-ph.GA↗

arXiv2011

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD)

We present first results from the "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD), a multi-configuration EVLA study of the neutral gas contents and dynamics of galaxies with HI masses in the 10^6-10^7 Solar mass range detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We describe the survey motivation and concept demonstration using VLA imaging of 6 low-mass galaxies detected in early ALFALFA data products. We then describe the primary scientific goals of SHIELD and present preliminary EVLA and WIYN 3.5m imaging of the 12 SHIELD galaxies. With only a few exceptions, the neutral gas distributions of these extremely low-mass galaxies are centrally concentrated. In only 1 system have we detected HI column densities higher than 10^21 cm^-2. Despite this, the stellar populations of all of these systems are dominated by blue stars. Further, we find ongoing star formation as traced by H alpha emission in 10 of the 11 galaxies with H alpha imaging obtained to date. Taken together these results suggest that extremely low-mass galaxies are forming stars in conditions different from those found in more massive systems. While detailed dynamical analysis requires the completion of data acquisition, the most well-resolved system is amenable to meaningful position-velocity analysis. For AGC 749237, we find well-ordered rotation of 30 km/s at a distance of ~40 arcseconds from the dynamical center. At the adopted distance of 3.2 Mpc, this implies the presence of a >1x10^8 Solar mass dark matter halo and a baryon fraction < ~0.1.

astro-ph.CO↗

arXiv2011

Optical Colors of Intracluster Light in the Virgo Cluster Core

We continue our deep optical imaging survey of the Virgo cluster using the CWRU Burrell Schmidt telescope by presenting B-band surface photometry of the core of the Virgo cluster in order to study the cluster's intracluster light (ICL). We find ICL features down to mu_b ~ 29 mag sq. arcsec, confirming the results of Mihos et al. (2005), who saw a vast web of low-surface brightness streams, arcs, plumes, and diffuse light in the Virgo cluster core using V-band imaging. By combining these two data sets, we are able to measure the optical colors of many of the cluster's low-surface brightness features. While much of our imaging area is contaminated by galactic cirrus, the cluster core near the cD galaxy, M87, is unobscured. We trace the color profile of M87 out to over 2000 arcsec, and find a blueing trend with radius, continuing out to the largest radii. Moreover, we have measured the colors of several ICL features which extend beyond M87's outermost reaches and find that they have similar colors to the M87's halo itself, B-V ~ 0.8. The common colors of these features suggests that the extended outer envelopes of cD galaxies, such as M87, may be formed from similar streams, created by tidal interactions within the cluster, that have since dissolved into a smooth background in the cluster potential.

astro-ph.CO↗