383 research outputs found
Discovery of Multi-Phase Cold Accretion in a Massive Galaxy at z=0.7
We present detailed photo+collisional ionization models and kinematic models
of the multi-phase absorbing gas, detected within the HST/COS, HST/STIS, and
Keck/HIRES spectra of the background quasar TON 153, at 104 kpc along the
projected minor axis of a star-forming spiral galaxy (z=0.6610). Complementary
g'r'i'Ks photometry and stellar population models indicate that the host galaxy
is dominated by a 4 Gyr stellar population with slightly greater than solar
metallicity and has an estimated log(M*)=11 and a log(Mvir)=13. Photoionization
models of the low ionization absorption, (MgI, SiII, MgII and CIII) which trace
the bulk of the hydrogen, constrain the multi-component gas to be cold
(logT=3.8-5.2) and metal poor (-1.68<[X/H]<-1.64). A lagging halo model
reproduces the low ionization absorption kinematics, suggesting gas coupled to
the disk angular momentum, consistent with cold accretion mode material in
simulations. The CIV and OVI absorption is best modeled in a separate
collisionally ionized metal-poor (-2.50<[X/H]<-1.93) warm phase with logT=5.3.
Although their kinematics are consistent with a wind model, given the 2-2.5dex
difference between the galaxy stellar metallicity and the absorption
metallicity indicates the gas cannot arise from galactic winds. We discuss and
conclude that although the quasar sight-line passes along the galaxy minor axis
at projected distance of 0.3 virial radii, well inside its virial shock radius,
the combination of the relative kinematics, temperatures, and relative
metallicities indicated that the multi-phase absorbing gas arises from cold
accretion around this massive galaxy. Our results appear to contradict recent
interpretations that absorption probing the projected minor axis of a galaxy is
sampling winds.Comment: 16 pages, 11 figures, accepted for publication in MNRA
MgII absorption systems with W_0 > 0.1 \AA for a radio selected sample of 77 QSOs and their associated magnetic fields at high redshifts
We present a catalogue of MgII absorption systems obtained from high
resolution UVES/VLT data of 77 QSOs in the redshift range 0.6 < z < 2.0, and
down to an equivalent width W_0 > 0.1 \AA. The statistical properties of our
sample are found to be in agreement with those from previous work in the
literature. However, we point out that the previously observed increase with
redshift of dN/dz for weak absorbers, pertains exclusively to very weak
absorbers with W_0 < 0.1 \AA. Instead, dN/dz for absorbers with W_0 in the
range 0.1-0.3 \AA actually decreases with redshift, similarly to the case of
strong absorbers. We then use this catalogue to extend our earlier analysis of
the links between the Faraday Rotation Measure of the quasars and the presence
of intervening MgII absorbing systems in their spectra. In contrast to the case
with strong MgII absorption systems W_0 > 0.3 \AA, the weaker systems do not
contribute significantly to the observed Rotation Measure of the background
quasars. This is possibly due to the higher impact parameters of the weak
systems compared to strong ones, suggesting that the high column density
magnetized material that is responsible for the Faraday Rotation is located
within about 50 kpc of the galaxies. Finally, we show that this result also
rules out the possibility that some unexpected secondary correlation between
the quasar redshift and its intrinsic Rotation Measure is responsible for the
association of high Rotation Measure and strong intervening MgII absorption
that we have presented elsewhere, since this would have produced an equal
effect for the weak absorption line systems, which exhibit a very similar
distribution of quasar redshifts.Comment: Accepted for publication in ApJ. 12 pages, 8 figure
Gas Accretion in Star-Forming Galaxies
Cold-mode gas accretion onto galaxies is a direct prediction of LCDM
simulations and provides galaxies with fuel that allows them to continue to
form stars over the lifetime of the Universe. Given its dramatic influence on a
galaxy's gas reservoir, gas accretion has to be largely responsible for how
galaxies form and evolve. Therefore, given the importance of gas accretion, it
is necessary to observe and quantify how these gas flows affect galaxy
evolution. However, observational data have yet to conclusively show that gas
accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is
a challenging endeavor and we now have obtained a significant amount of
observational evidence to support it. This chapter reviews the current
observational evidence of gas accretion onto star-forming 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
Springer. This chapter includes 22 pages with 7 Figure
ZFOURGE: Extreme 5007 emission may be a common early-lifetime phase for star-forming galaxies at
Using the \prospector\ spectral energy distribution (SED) fitting code, we
analyze the properties of 19 Extreme Emission Line Galaxies (EELGs) identified
in the bluest composite SED in the \zfourge\ survey at .
\prospector\ includes a physical model for nebular emission and returns
probability distributions for stellar mass, stellar metallicity, dust
attenuation, and nonparametric star formation history (SFH). The EELGs show
evidence for a starburst in the most recent 50 Myr, with the median EELG having
a specific star formation rate (sSFR) of 4.6 Gyr and forming 15\% of its
mass in this short time. For a sample of more typical star-forming galaxies
(SFGs) at the same redshifts, the median SFG has a sSFR of 1.1 Gyr and
forms only of its mass in the last 50 Myr. We find that virtually all of
our EELGs have rising SFHs, while most of our SFGs do not. From our analysis,
we hypothesize that many, if not most, star-forming galaxies at
undergo an extreme H+[\hbox{{\rm O}\kern 0.1em{\sc iii}}] emission
line phase early in their lifetimes. In a companion paper, we obtain
spectroscopic confirmation of the EELGs as part of our {\sc MOSEL} survey. In
the future, explorations of uncertainties in modeling the UV slope for galaxies
at are needed to better constrain their properties, e.g. stellar
metallicities.Comment: 11 pages, 5 figures (main figure is fig 5), accepted for publication
in Ap
On the Heterogeneity of Metal-Line and Ly-Alpha Absorption in Galaxy "Halos" at z~0.7
We examine the properties of two galaxy "halos" at z ~ 0.7 in the TON 153
(z_em = 1.01) quasar field. The first absorber-galaxy pair (G1) is a z = 0.672,
L_B = 4.3 L*_B, E/S0 galaxy probed at D = 58 kpc. G1 is associated with a
remarkable five-component Ly-alpha complex having tau_LL < 0.4, W_r(Lya) = 2.8
A, and a velocity spread of v = 1420 km/s. We find no MgII, CIV, NV, nor OVI
absorption in these clouds and infer metallicity upper limits of -3 <
log(Z/Z_sun) < -1, depending upon assumptions of photoionized or collisionally
ionized gas. The second absorber-galaxy pair (G2) is a z = 0.661, L_B = 1.8
L*_B, Sab galaxy probed at D = 103 kpc. G2 is associated with metal--enriched
(log Z/Z_sun ~ -0.4) photoionized gas having N(HI) ~ 18.3 and a velocity spread
of v = 200 km/s. The very different G1 and G2 systems both have gas-galaxy
properties inconsistent with the standard luminosity dependent galaxy "halo"
model commonly invoked for quasar absorption line surveys. We emphasize that
mounting evidence is revealing that extended galactic gaseous envelopes in the
regime of D < 100 kpc do not exhibit a level of homogeneity supporting a
standardized halo model. Selection effects may have played a central role in
the development of a simple model. We discuss the G1 and G2 systems in the
context of Lambda-CDM models of galaxy formation and suggest that the
heterogeneous properties of absorber-galaxy pairs is likely related to the
range of overdensities from which galaxies and gas structures arise.Comment: 5 pages, 2 figures, Accepted to Ap
A Correlation Between Galaxy Morphology and MgII Halo Absorption Strength
(Abridged) We compared the quantified morphological properties of 37
intermediate redshift MgII absorption selected galaxies to the properties of
the absorbing halo gas, observed in the spectra of background quasars. The
galaxy morphologies were measured using GIM2D modeling of Hubble Space
Telescope WFPC-2 images and the absorbing gas properties were obtained from
HIRES/Keck and UVES/VLT quasar spectra. We found a 3.1 sigma correlation
between galaxy morphological asymmetries normalized by the quasar-galaxy
projected separations, A/D, and the MgII rest-frame equivalent widths.
Saturation effects cause increased scatter in the relationship with increasing
W_r(2796). We defined a subsample for which the fraction of saturated pixels in
the absorption profiles is f_sat<0.5. The correlation strengthened to 3.3
sigma. We also find a paucity of small morphological asymmetries for galaxies
selected by MgII absorption as compared to those of the general population of
field galaxies, as measured in the Medium Deep Survey. The K-S probability that
the two samples are drawn from the same galaxy population is ruled out at a
99.8% confidence level. The A/D-W_r(2796) correlation suggests a connection
between the processes that perturb galaxies and the quantity of gas in their
halos, normalized by the impact parameter. Since the perturbations are minor,
it is clear that dramatic processes or events are not required for a galaxy to
have an extended halo; the galaxies appear "normal". We suggest that common,
more mild processes that populate halos with gas, such as satellite galaxy
merging, accretion of the local cosmic web, and longer-range galaxy-galaxy
interactions, consequently also induce the observed minor perturbations in the
galaxies.Comment: Accepted for publication in the Astrophysical Journa
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
Non variability of intervening absorbers observed in the UVES spectra of the "naked-eye" GRB080319
The aim of this paper is to investigate the properties of the intervening
absorbers lying along the line of sight of Gamma-Ray Burst (GRB) 080319B
through the analysis of its optical absorption features. To this purpose, we
analyze a multi-epoch, high resolution spectroscopic observations (R=40000,
corresponding to 7.5 km/s) of the optical afterglow of GRB080319B (z=0.937),
taken with UVES at the VLT. Thanks to the rapid response mode (RRM), we
observed the afterglow just 8m:30s after the GRB onset when the magnitude was R
~ 12. This allowed us to obtain the best signal-to-noise, high resolution
spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). Two further
RRM and target of opportunity observations were obtained starting 1.0 and 2.4
hours after the event, respectively. Four MgII absorption systems lying along
the line of sight to the afterglow have been detected in the redshift range 0.5
< z < 0.8, most of them showing a complex structure featuring several
components. Absorptions due to FeII, MgI and MnII are also present; they appear
in four, two and one intervening absorbers, respectively. One out of four
systems show a MgII2796 rest frame equivalent width larger than 1A. This
confirms the excess of strong MgII absorbers compared to quasars, with dn/dz =
0.9, ~ 4 times larger than the one observed along quasar lines of sight. In
addition, the analysis of multi-epoch, high-resolution spectra allowed us to
exclude a significant variability in the column density of the single
components of each absorber. Combining this result with estimates of the size
of the emitting region, we can reject the hypothesis that the difference
between GRB and QSO MgII absorbers is due to a different size of the emitting
regions.Comment: 10 pages, 15 ps figures, submitted to MNRA
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