48 research outputs found
HI in Virgo's "Red and Dead" Dwarf Ellipticals - A Tidal Tail and Central Star Formation
We investigate a sample of 3 dwarf elliptical galaxies in the Virgo Cluster
which have significant reservoirs of HI. We present deep optical imaging (from
CFHT and KPNO), HI spectra (Arecibo) and resolved HI imaging (VLA) of this
sample. These observations confirm their HI content and optical morphologies,
and indicate that the gas is unlikely to be recently accreted. The sample has
more in common with dwarf transitionals, although dwarf transitionals are
generally lower in stellar mass and gas fraction. VCC 190 has an HI tidal tail
from a recent encounter with the massive spiral galaxy NGC 4224. In VCC 611,
blue star-forming features are observed which were unseen by shallower SDSS
imaging.Comment: 11 pages, 6 figures, accepted in A
ALFALFA and WSRT Imaging of Extended H I Features in the Leo Cloud of Galaxies
We present ALFALFA HI observations of a well studied region of the Leo Cloud,
which includes the NGC 3227 group and the NGC 3190 group. We detect optically
dark HI tails and plumes with extents potentially exceeding 600 kpc, well
beyond the field of view of previous observations. These HI features contain
approximately 40% of the total HI mass in the NGC~3227 group and 10% in the
NGC~3190 group. We also present WSRT maps which show the complex morphology of
the extended emission in the NGC~3227 group. We comment on previously proposed
models of the interactions in these groups and the implications for the scale
of group processing through interactions. Motivated by the extent of the HI
plumes, we place the HI observations in the context of the larger loose group,
demonstrating the need for future sensitive, wide field HI surveys to
understand the role of group processing in galaxy evolution.Comment: 17 pages, 9 figures, accepted for publication in MNRA
H I in group interactions: HCG 44
Extending deep observations of the neutral atomic hydrogen (HI) to the
environment around galaxy groups can reveal a complex history of group
interactions which is invisible to studies that focus on the stellar component.
Hickson Compact Group 44 (HCG 44) is a nearby example and we have combined HI
data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and
Arecibo Legacy Fast ALFA survey, in order to achieve high column density
sensitivity (N_HI < 2x10^18 cm^-2) to the neutral gas over a large
field-of-view beyond the compact group itself. We find the giant HI tail north
of HCG 44 contains 1.1x10^9 M_Sun of gas and extends 450 kpc from the compact
group: twice as much mass and 33% further than previously detected. However,
the additional gas is still unable to account for the known HI deficiency of
HCG 44. The tail likely formed through a strong tidal interaction and HI clouds
in the tail have survived for 1 Gyr or more after being stripped. This has
important implications for understanding the survival of neutral clouds in the
intragroup and circumgroup medium, and we discuss their survival in the context
of simulations of cold gas in hot halos. HCG 44 is one of a growing number of
galaxy groups found to have more extended HI in the intragroup and circumgroup
medium than previously measured. Our results provide constraints for
simulations on the properties of galaxy group halos, and reveal a glimpse of
what will be seen by future powerful HI telescopes and surveys.Comment: 12 pages, 6 figures. Accepted for publication in MNRA
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 .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) < 9.51] and HI mass to B-band luminosity ratios (3 <
M/L < 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)Comment: Astronomical Journal, in pres
Gas-rich, field ultra-diffuse galaxies host few globular clusters
We present Hubble Space Telescope imaging of 14 gas-rich, low surface
brightness and ultra-diffuse galaxies (UDGs) in the field at distances of 25-36
Mpc. An inspection of point-like sources brighter than the turnover magnitude
of the globular cluster luminosity function and within twice the half-light
radii of each galaxy reveals that, unlike those in denser environments,
gas-rich, field UDGs host very few old globular clusters (GCs). Most of the
targets (nine) have zero candidate GCs, with the remainder having one or two
candidates each. These findings are broadly consistent with expectations for
normal dwarf galaxies of similar stellar mass. This rules out gas-rich, field
UDGs as potential progenitors of the GC-rich UDGs that are typically found in
galaxy clusters. However, some in galaxy groups may be directly accreted from
the field. In line with other recent results, this strongly suggests that there
must be at least two distinct formation pathways for UDGs, and that this
sub-population is simply an extreme low surface brightness extension of the
underlying dwarf galaxy population. The root cause of their diffuse stellar
distributions remains unclear, but the formation mechanism appears to only
impact the distribution of stars (and potentially dark matter), without
strongly impacting the distribution of neutral gas, the overall stellar mass,
or the number of GCs.Comment: Submitted to AAS journal
The Intrinsic Shapes of Low Surface Brightness Galaxies (LSBGs):A Discriminant of LSBG Galaxy Formation Mechanisms
We use the low surface brightness galaxy (LSBG) samples created from the Hyper Suprime-Cam Subaru Strategic Program (781 galaxies), the Dark Energy Survey (20977 galaxies), and the Legacy Survey (selected via H I detection in the Arecibo Legacy Fast ALFA Survey, 188 galaxies) to infer the intrinsic shape distribution of the LSBG population. To take into account the effect of the surface brightness cuts employed when constructing LSBG samples, we simultaneously model both the projected ellipticity and the apparent surface brightness in our shape inference. We find that the LSBG samples are well characterized by oblate spheroids, with no significant difference between red and blue LSBGs. This inferred shape distribution is in good agreement with similar inferences made for ultra-diffuse cluster galaxy samples, indicating that environment does not play a key role in determining the intrinsic shape of LSBGs. We also find some evidence that LSBGs are more thickened than similarly massive high surface brightness dwarfs. We compare our results to intrinsic shape measures from contemporary cosmological simulations, and find that the observed LSBG intrinsic shapes place considerable constraints on the formation path of such galaxies. In particular, LSBG production via the migration of star formation to large radii produces intrinsic shapes in good agreement with our observational findings
The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging
We present Hubble Space Telescope (HST) observations of the low surface
brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo
Legacy Fast ALFA HI survey and was cataloged as an (almost) dark galaxy because
it did not exhibit any obvious optical counterpart in the available survey data
(e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an
ultra-low SB stellar component located at the center of the HI detection. We
use the HST images to produce a deep color-magnitude diagram (CMD) of the
resolved stellar population present in Coma P. We clearly detect a red stellar
sequence that we interpret to be a red giant branch, and use it to infer a tip
of the red giant branch (TRGB) distance of 5.50 Mpc. The new
distance is substantially lower than earlier estimates and shows that Coma P is
an extreme dwarf galaxy. Our derived stellar mass is only 4.3 10
, meaning that Coma P has an extreme HI-to-stellar mass ratio of 81.
We present a detailed analysis of the galaxy environment within which Coma P
resides. We hypothesize that Coma P formed within a local void and has spent
most of its lifetime in a low-density environment. Over time, the gravitational
attraction of the galaxies located in the void wall has moved it to the edge,
where it had a recent "fly-by" interaction with M64. We investigate the
possibility that Coma P is at a farther distance and conclude that the
available data are best fit by a distance of 5.5 Mpc.Comment: 22 pages, 11 figures. Accepted for publication in the Astronomical
Journa