81 research outputs found
Cold gas mass measurements for the era of large optical spectroscopic surveys
Gas plays an important role in many processes in galaxy formation and
evolution, but quantifying the importance of gas has been hindered by the
challenge to measure gas masses for large samples of galaxies. Datasets of
direct atomic and molecular gas measurements are sufficient to establish simple
scaling relations, but often not large enough to quantify three-parameter
relations, or second order dependencies. As an alternative approach, we derive
here indirect cold gas measurements from optical emission lines using
photoionization models for galaxies in the SDSS main galaxy sample and the
PHANGS-MUSE survey. We calibrate the gas surface density measurements using
xCOLD GASS and PHANGS-ALMA molecular gas measurements to ensure our
measurements are reliable. We demonstrate the importance of taking into account
the scale-dependence of the relation between optical depth () and gas
surface density () and provide a general prescription to estimate
from , metallicity and the dust-to-metal ratio, at any
arbitrary physical resolution. To demonstrate that the indirect cold gas masses
are accurate enough to quantify the role of gas in galaxy evolution, we study
the mass-metallicity relation (MZR) of SDSS galaxies and show that as a third
parameter, gas mass is better than SFR at reducing the scatter of the relation,
as predicted by models and simulations.Comment: 15 pages, 12 figures, 3 tables, submitted to MNRA
The Arecibo Legacy Fast ALFA Survey: IV. Strategies for Signal Identification and Survey Catalog Reliability
We present a signal extraction utility written for the purposes of the
Arecibo Legacy Fast ALFA survey (ALFALFA). This survey, when completed, will
have covered 7000 square degrees of the high galactic latitude sky and should
detect over 20,000 extragalactic objects. It is the most sensitive blind HI
survey to date. The large size of the survey justifies in itself the need for
an automated way of identifying signals in the data set. The matched-filtering
signal extractor proposed is based on convolutions in the Fourier domain of
templates of varying widths with each spectrum. The chosen templates are built
from a simple combination of Hermite functions to mimic the shape of typical
galactic HI profiles of varying widths. The main advantages of this
matched-filtering approach are a sensitivity to the total flux of the signals
(and not only to peak flux), robustness against instabilities and short
computing times. The details of the algorithm are given here, as well as
results of simulations that assess the reliability and completeness of the
process.Comment: 10 pages, 8 figures, accepted for publication in the Astronomical
Journal. Higher resolution figures available at
http://egg.astro.cornell.edu/alfalfa/index.ph
The Arecibo Legacy Fast ALFA Survey: VIII. HI Source Catalog of the Anti-Virgo Region at dec = +25 deg
We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA
(ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of
the sky having 22h < R.A. < 03h and 24 deg < Dec. < 26 deg . This complements a
previous catalog in the region 26 deg < Dec. < 28 deg (Saintonge et al. 2008).
We present here the detections falling into three classes: (a) extragalactic
sources with S/N > 6.5, where the reliability of the catalog is better than
95%; (b) extragalactic sources 5.0 < S/N < 6.5 and a previously measured
optical redshift that corroborates our detection; or (c) High Velocity Clouds
(HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of
the 541 objects presented here, 90 are associated with High Velocity Clouds,
while the remaining 451 are identified as extragalactic objects. Optical
counterparts have been matched with all but one of the extragalactic objects.Comment: 26 pages, 5 figures, 1 table, accepted for publication in
Astrophysical Journal Supplement Serie
The recent star formation history of NGC 628 on resolved scales
Star formation histories (SFHs) are integral to our understanding of galaxy evolution. We can study recent SFHs by comparing the star formation rate (SFR) calculated using different tracers, as each probes a different timescale. We aim to calibrate a proxy for the present-day rate of change in SFR, dSFR/dt, which does not require full spectral energy distribution (SED) modeling and depends on as few observables as possible, to guarantee its broad applicability. To achieve this, we create a set of models in CIGALE and define a SFR change diagnostic as the ratio of the SFR averaged over the past 5 and 200 Myr, ⟨SFR5⟩/⟨SFR200⟩, probed by the Hα −FUV colour. We apply ⟨SFR5⟩/⟨SFR200⟩ to the nearby spiral NGC 628 and find that its star formation activity has overall been declining in the recent past, with the spiral arms, however, maintaining a higher level of activity. The impact of the spiral arm structure is observed to be stronger on ⟨SFR5⟩/⟨SFR200⟩ than on the star formation efficiency (SFEH2). In addition, increasing disk pressure tends to increase recent star formation, and consequently ⟨SFR5⟩/⟨SFR200⟩. We conclude that ⟨SFR5⟩/⟨SFR200⟩ is sensitive to the molecular gas content, spiral arm structure, and disk pressure. The ⟨SFR5⟩/⟨SFR200⟩ indicator is general and can be used to reconstruct the recent SFH of any star-forming galaxy for which Hα, FUV, and either mid- or far-IR photometry is available, without the need of detailed modeling
How to quench a galaxy
We show how the interplay between active galactic nuclei (AGN) and merger
history determines whether a galaxy quenches star formation at high redshift.
We first simulate, in a full cosmological context, a galaxy of total dynamical
mass at . Then we systematically alter the accretion
history of the galaxy by minimally changing the linear overdensity in the
initial conditions. This "genetic modification" approach allows the generation
of three sets of CDM initial conditions leading to maximum merger
ratios of 1:10, 1:5 and 2:3 respectively. The changes leave the final halo
mass, large scale structure and local environment unchanged, providing a
controlled numerical experiment. Interaction between the AGN physics and
mergers in the three cases lead respectively to a star-forming,
temporarily-quenched and permanently-quenched galaxy. However the differences
do not primarily lie in the black hole accretion rates, but in the kinetic
effects of the merger: the galaxy is resilient against AGN feedback unless its
gaseous disk is first disrupted. Typical accretion rates are comparable in the
three cases, falling below yr, equivalent to around
of the Eddington rate or times the pre-quenching star formation
rate, in agreement with observations. This low level of black hole accretion
can be sustained even when there is insufficient dense cold gas for star
formation. Conversely, supernova feedback is too distributed to generate
outflows in high-mass systems, and cannot maintain quenching over periods
longer than the halo gas cooling time.Comment: Clarifications and added references; accepted for publication in
MNRA
The Arecibo Legacy Fast ALFA Survey: VI. Second HI Source Catalog of the Virgo Cluster Region
We present the third installment of HI sources extracted from the Arecibo
Legacy Fast ALFA extragalactic survey. This dataset continues the work of the
Virgo ALFALFA catalog. The catalogs and spectra published here consist of data
obtained during the 2005 and 2006 observing sessions of the survey. The catalog
consists of 578 HI detections within the range 11h 36m < R.A.(J2000) < 13h 52m
and +08 deg < Dec.(J2000) < +12 deg, and cz_sun < 18000 km/s. The catalog
entries are identified with optical counterparts where possible through the
examination of digitized optical images. The catalog detections can be
classified into three categories: (a) detections of high reliability with S/N >
6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c)
signals of lower S/N which coincide spatially with an optical object and known
redshift. 75% of the sources are newly published HI detections. Of particular
note is a complex of HI clouds projected between M87 and M49 that do not
coincide with any optical counterparts. Candidate objects without optical
counterparts are few. The median redshift for this sample is 6500 km/s and the
cz distribution exhibits the local large scale structure consisting of Virgo
and the background void and the A1367-Coma supercluster regime at cz_sun ~7000
km/s. Position corrections for telescope pointing errors are applied to the
dataset by comparing ALFALFA continuum centroid with those cataloged in the
NRAO VLA Sky Survey. The uncorrected positional accuracy averages
27 arcsec ~(21 arcsec ~median) for all sources with S/N > 6.5 and is of order
~21 arcsec ~(16 arcsec ~median) for signals with S/N > 12. Uncertainties in
distances toward the Virgo cluster can affect the calculated HI mass
distribution.Comment: 25 pages, 1 Table, 8 figures, Accepted by the Astronomical Journa
HIghMass - High HI Mass, HI-Rich Galaxies at : Combined HI and H Observations
We present resolved HI and CO observations of three galaxies from the
HIghMass sample, a sample of HI-massive (), gas-rich
( in top for their ) galaxies identified in the ALFALFA
survey. Despite their high gas fractions, these are not low surface brightness
galaxies, and have typical specific star formation rates (SFR) for their
stellar masses. The three galaxies have normal star formation rates for their
HI masses, but unusually short star formation efficiency scale lengths,
indicating that the star formation bottleneck in these galaxies is in the
conversion of HI to H, not in converting H to stars. In addition, their
dark matter spin parameters () are above average, but not
exceptionally high, suggesting that their star formation has been suppressed
over cosmic time but are now becoming active, in agreement with prior H
observations.Comment: 20 pages, 13 figure
Outflows in Star-forming Galaxies: Stacking Analyses of Resolved Winds and the Relation to Their Hosts' Properties
Outflows form an integral component in regulating the gas cycling in and out
of galaxies, although their impact on the galaxy hosts is still poorly
understood. Here we present an analysis of 405 high mass (log
M/M), star-forming galaxies (excluding AGN) with low
inclinations at 0, using stacking techniques of the NaD
5889,5895 A neutral gas tracer in IFU observations from the
MaNGA DR15 survey. We detect outflows in the central regions of 78/405 galaxies
and determine their extent and power through the construction of stacked
annuli. We find outflows are most powerful in central regions and extend out to
1R, with declining mass outflow rates and loading factors as a
function of radius. The stacking of spaxels over key galaxy quantities reveals
outflow detections in regions of high (0.01
Myrkpc) and (10
Mkpc) along the resolved main sequence. Clear correlations
with suggest it is the main regulator of outflows, with a
critical threshold of 0.01 Myrkpc needed to
escape the weight of the disk and launch them. Furthermore, measurements of the
H and D4000 indices reveal virtually identical star formation
histories between galaxies with outflows and those without. Finally, through
stacking of HI 21 cm observations for a subset of our sample, we find outflow
galaxies show reduced HI gas fractions at central velocities compared to their
non-detection control counterparts, suggestive of some removal of HI gas,
likely in the central regions of the galaxies, but not enough to completely
quench the host.Comment: 20 pages, 11 figures. Accepted for publication in MNRA
EDGE: The origin of scatter in ultra-faint dwarf stellar masses and surface brightnesses
We demonstrate how the least luminous galaxies in the Universe, ultra-faint
dwarf galaxies, are sensitive to their dynamical mass at the time of cosmic
reionization. We select a low-mass () dark matter halo from a cosmological volume, and perform
zoom hydrodynamical simulations with multiple alternative histories using
"genetically modified" initial conditions. Earlier forming ultra-faints have
higher stellar mass today, due to a longer period of star formation before
their quenching by reionization. Our histories all converge to the same final
dynamical mass, demonstrating the existence of extended scatter ( 1 dex)
in stellar masses at fixed halo mass due to the diversity of possible
histories. One of our variants builds less than 2 % of its final dynamical mass
before reionization, rapidly quenching in-situ star formation. The bulk of its
final stellar mass is later grown by dry mergers, depositing stars in the
galaxy's outskirts and hence expanding its effective radius. This mechanism
constitutes a new formation scenario for highly diffuse (, ), metal-poor (), ultra-faint ()
dwarf galaxies within the reach of next-generation low surface brightness
surveys.Comment: Minor edits to match the published ApJL version. Results unchange
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