248 research outputs found
The Survey for Ionization in Neutral Gas Galaxies- II. The Star Formation Rate Density of the Local Universe
We derive observed Halpha and R band luminosity densities of an HI-selected
sample of nearby galaxies using the SINGG sample to be l_Halpha' = (9.4 +/-
1.8)e38 h_70 erg s^-1 Mpc^-3 for Halpha and l_R' = (4.4 +/- 0.7)e37 h_70 erg
s^-1 A^-1 Mpc^-3 in the R band. This R band luminosity density is approximately
70% of that found by the Sloan Digital Sky Survey. This leads to a local star
formation rate density of log(SFRD) = -1.80 +0.13/-0.07(random) +/-
0.03(systematic) + log(h_70) after applying a mean internal extinction
correction of 0.82 magnitudes. The gas cycling time of this sample is found to
be t_gas = 7.5 +1.3/-2.1 Gyr, and the volume-averaged equivalent width of the
SINGG galaxies is EW(Halpha) = 28.8 +7.2/-4.7 A (21.2 +4.2/-3.5 A without
internal dust correction). As with similar surveys, these results imply that
SFRD(z) decreases drastically from z ~ 1.5 to the present. A comparison of the
dynamical masses of the SINGG galaxies evaluated at their optical limits with
their stellar and HI masses shows significant evidence of downsizing: the most
massive galaxies have a larger fraction of their mass locked up in stars
compared with HI, while the opposite is true for less massive galaxies. We show
that the application of the Kennicutt star formation law to a galaxy having the
median orbital time at the optical limit of this sample results in a star
formation rate decay with cosmic time similar to that given by the SFRD(z)
evolution. This implies that the SFRD(z) evolution is primarily due to the
secular evolution of galaxies, rather than interactions or mergers. This is
consistent with the morphologies predominantly seen in the SINGG sample.Comment: 15 pages, 5 figures, ApJ in press. Data available at
http://sungg.pha.jhu.edu/PubData/ Corrected: Minor typos and formatting
issues fixe
The Survey for Ionization in Neutral Gas Galaxies: I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG), a
census of star formation in HI-selected galaxies. The survey consists of
H-alpha and R-band imaging of a sample of 468 galaxies selected from the HI
Parkes All Sky Survey (HIPASS). The sample spans three decades in HI mass and
is free of many of the biases that affect other star forming galaxy samples. We
present the criteria for sample selection, list the entire sample, discuss our
observational techniques, and describe the data reduction and calibration
methods. This paper focuses on 93 SINGG targets whose observations have been
fully reduced and analyzed to date. The majority of these show a single
Emission Line Galaxy (ELG). We see multiple ELGs in 13 fields, with up to four
ELGs in a single field. All of the targets in this sample are detected in
H-alpha indicating that dormant (non-star forming) galaxies with M(HI) > ~3e7
M_sun are very rare. A database of the measured global properties of the ELGs
is presented. The ELG sample spans four orders of magnitude in luminosity
(H-alpha and R-band), and H-alpha surface brightness, nearly three orders of
magnitude in R surface brightness and nearly two orders of magnitude in H-alpha
equivalent width (EW). The surface brightness distribution of our sample is
broader than that of the Sloan Digital Sky Survey spectroscopic sample, the
(EW) distribution is broader than prism-selected samples, and the morphologies
found include all common types of star forming galaxies (e.g. irregular,
spiral, blue compact dwarf, starbursts, merging and colliding systems, and even
residual star formation in S0 and Sa spirals). (abridged)Comment: 28 pages, ApJS, in press. Full resolution version with all panels of
Fig. 8 available at http://sungg.pha.jhu.edu/publications.html . On line data
available at http://sungg.pha.jhu.edu/PubData/ . Author list corrected. Wrong
value for f_ap used in eq. 7 now corrected; typos corrected, non-used
references replaced, others update
On the Kinematics of Cold, Metal-enriched Galactic Fountain Flows in Nearby Star-forming Galaxies
We use medium-resolution Keck/Echellette Spectrograph and Imager spectroscopy
of bright quasars to study cool gas traced by CaII 3934,3969 and NaI 5891,5897
absorption in the interstellar/circumgalactic media of 21 foreground
star-forming galaxies at redshifts 0.03 < z < 0.20 with stellar masses 7.4 <
log M_*/M_sun < 10.6. The quasar-galaxy pairs were drawn from a unique sample
of Sloan Digital Sky Survey quasar spectra with intervening nebular emission,
and thus have exceptionally close impact parameters (R_perp < 13 kpc). The
strength of this line emission implies that the galaxies' star formation rates
(SFRs) span a broad range, with several lying well above the star-forming
sequence. We use Voigt profile modeling to derive column densities and
component velocities for each absorber, finding that column densities N(CaII) >
10^12.5 cm^-2 (N(NaI) > 10^12.0 cm^-2) occur with an incidence f_C(CaII) =
0.63^+0.10_-0.11 (f_C(NaI) = 0.57^+0.10_-0.11). We find no evidence for a
dependence of f_C or the rest-frame equivalent widths W_r(CaII K) or W_r(NaI
5891) on R_perp or M_*. Instead, W_r(CaII K) is correlated with local SFR at
>3sigma significance, suggesting that CaII traces star formation-driven
outflows. While most of the absorbers have velocities within +/-50 km/s of the
host redshift, their velocity widths (characterized by Delta v_90) are
universally 30-177 km/s larger than that implied by tilted-ring modeling of the
velocities of interstellar material. These kinematics must trace galactic
fountain flows and demonstrate that they persist at R_perp > 5 kpc. Finally, we
assess the relationship between dust reddening and W_r(CaII K) (W_r(NaI 5891)),
finding that 33% (24%) of the absorbers are inconsistent with the best-fit
Milky Way E(B-V)-W_r relations at >3sigma significance.Comment: 38 pages, 16 figures, 4 tables. Accepted to Ap
Gas Accretion via Lyman Limit Systems
In cosmological simulations, a large fraction of the partial Lyman limit
systems (pLLSs; 16<log N(HI)<17.2) and LLSs (17.2log N(HI)<19) probes
large-scale flows in and out of galaxies through their circumgalactic medium
(CGM). The overall low metallicity of the cold gaseous streams feeding galaxies
seen in these simulations is the key to differentiating them from metal rich
gas that is either outflowing or being recycled. In recent years, several
groups have empirically determined an entirely new wealth of information on the
pLLSs and LLSs over a wide range of redshifts. A major focus of the recent
research has been to empirically determine the metallicity distribution of the
gas probed by pLLSs and LLSs in sizable and representative samples at both low
(z2) redshifts. Here I discuss unambiguous evidence for
metal-poor gas at all z probed by the pLLSs and LLSs. At z<1, all the pLLSs and
LLSs so far studied are located in the CGM of galaxies with projected distances
<100-200 kpc. Regardless of the exact origin of the low-metallicity pLLSs/LLSs,
there is a significant mass of cool, dense, low-metallicity gas in the CGM that
may be available as fuel for continuing star formation in galaxies over cosmic
time. As such, the metal-poor pLLSs and LLSs are currently among the best
observational evidence of cold, metal-poor gas accretion onto galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
Gas Accretion Traced in Absorption in Galaxy Spectroscopy
The positive velocity shift of absorption transitions tracing diffuse
material observed in a galaxy spectrum is an unambiguous signature of gas flow
toward the host system. Spectroscopy probing, e.g., NaI D resonance lines in
the rest-frame optical or MgII and FeII in the near-ultraviolet is in principle
sensitive to the infall of cool material at temperatures ~ 100-10,000 K
anywhere along the line of sight to a galaxy's stellar component. However,
secure detections of this redshifted absorption signature have proved
challenging to obtain due to the ubiquity of cool gas outflows giving rise to
blueshifted absorption along the same sightlines. In this chapter, we review
the bona fide detections of this phenomenon. Analysis of NaI D line profiles
has revealed numerous instances of redshifted absorption observed toward
early-type and/or AGN-host galaxies, while spectroscopy of MgII and FeII has
provided evidence for ongoing gas accretion onto >5% of luminous, star-forming
galaxies at z ~ 0.5-1. We then discuss the potentially ground-breaking benefits
of future efforts to improve the spectral resolution of such studies, and to
leverage spatially-resolved spectroscopy for new constraints on inflowing gas
morphology.Comment: 21 pages, 7 figures. Invited review to appear in Gas Accretion onto
Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e,
to be published by Springe
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
Circumgalactic Gas and the Precipitation Limit
During the last decade, numerous and varied observations, along with
increasingly sophisticated numerical simulations, have awakened astronomers to
the central role the circumgalactic medium (CGM) plays in regulating galaxy
evolution. It contains the majority of the baryonic matter associated with a
galaxy, along with most of the metals, and must continually replenish the star
forming gas in galaxies that continue to sustain star formation. And while the
CGM is complex, containing gas ranging over orders of magnitude in temperature
and density, a simple emergent property may be governing its structure and
role. Observations increasingly suggest that the ambient CGM pressure cannot
exceed the limit at which cold clouds start to condense out and precipitate
toward the center of the potential well. If feedback fueled by those clouds
then heats the CGM and causes it to expand, the pressure will drop and the
"rain" will diminish. Such a feedback loop tends to suspend the CGM at the
threshold pressure for precipitation. The coming decade will offer many
opportunities to test this potentially fundamental principle of galaxy
evolution.Comment: Astro2020 White Paper, 8 pages, 2 figures (differences from Astro2020
version: some typos fixed, some references added
IMAGES I. Strong evolution of galaxy kinematics since z=1
(abbreviated) We present the first results of the ESO large program,
``IMAGES'' which aims at obtaining robust measurements of the kinematics of
distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D
spectroscopy is essential to robustly measure the often distorted kinematics of
distant galaxies (e.g., Flores et al. 2006). We derive the velocity fields and
-maps of 36 galaxies at 0.4<z<0.75 from the kinematics of the [OII]
emission line doublet, and generate a robust technique to identify the nature
of the velocity fields based on the pixels of the highest signal-to-noise
ratios (S/N). We have gathered a unique sample of 63 velocity fields of
emission line galaxies (W0([OII]) > 15 A) at z=0.4-0.75, which are a
representative subsample of the population of M_stellar>1.5x10^{10} M_sun
emission line galaxies in this redshift range, and are largely unaffected by
cosmic variance. Taking into account all galaxies -with or without emission
lines- in that redshift range, we find that at least 41+/-7% of them have
anomalous kinematics, i.e., they are not dynamically relaxed. This includes
26+/-7% of distant galaxies with complex kinematics, i.e., they are not simply
pressure or rotationally supported. Our result implies that galaxy kinematics
are among the most rapidly evolving properties, because locally, only a few
percent of the galaxies in this mass range have complex kinematics.Comment: 17 pages, 6 figures, Accepted by A&
Nearby early-type galaxies with ionized gas. The UV emission from GALEX observations
We present GALEX far-ultraviolet (FUV, =1538 \AA) and
near-ultraviolet (NUV, =2316 \AA) surface photometry of 40
early-type galaxies (ETGs) selected from a wider sample of 65 nearby ETGs
showing emission lines in their optical spectra. We derive FUV and NUV surface
brightness profiles, (FUV-NUV) colour profiles and D integrated
magnitudes. We extend the photometric study to the optical {\it r} band from
SDSS imaging for 14 of these ETGs. In general, the (FUV-NUV) radial colour
profiles become redder with galactocentric distance in both rejuvenated ( Gyr) and old ETGs. Colour profiles of NGC 1533, NGC 2962, NGC 2974, NGC
3489, and IC 5063 show rings and/or arm-like structures, bluer than the body of
the galaxy, suggesting the presence of recent star formation. Although seven of
our ETGs show shell systems in their optical image, only NGC 7135 displays
shells in the UV bands. We characterize the UV and optical surface brightness
profiles, along the major axis, using a Sersic law. The Sersic law exponent,
, varies from 1 to 16 in the UV bands. S0 galaxies tend to have lower values
of (). The Sersic law exponent seems to be a watershed: ETGs
with tend to have [/Fe] greater than 0.15, implying a short
star-formation time scale. We find a significant correlation between the
FUVNUV colour and central velocity dispersions , with the UV colours
getting bluer at larger . This trend is likely driven by a combined
effect of `downsizing' and of the mass-metallicity relation.Comment: Accepted for publication in MNRAS, 33 pages, 7 figure
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