144 research outputs found
The prevalence and properties of cold gas inflows and outflows around galaxies in the local Universe
We perform a stacking analysis of the neutral
\nad\,5889,5895\,\AA\ ISM doublet using the SDSS DR7
spectroscopic data set to probe the prevalence and characteristics of cold
(T\,\,10\,K) galactic-scale gas flows in local (0.0250.1) inactive and AGN-host galaxies across the SFR-M plane. We
find low-velocity outflows to be prevalent in regions of high SFRs and stellar
masses (10 log M/M 11.5), however we do
not find any detections in the low mass (log M/M 10)
regime. We also find tentative detections of inflowing gas in high mass
galaxies across the star-forming population. We derive mass outflow rates in
the range of 0.14-1.74\,Myr and upper limits on inflow rates
<1\,Myr, allowing us to place constraints on the mass loading
factor (=/SFR) for use in simulations of the local
Universe. We discuss the fate of the outflows by comparing the force provided
by the starburst to the critical force needed to push the outflow outward, and
find the vast majority of the outflows unlikely to escape the host system.
Finally, as outflow detection rates and central velocities do not vary strongly
with the presence of a (weak) active supermassive black hole, we determine that
star formation appears to be the primary driver of outflows at 0.Comment: Accepted in MNRAS. 36 pages, 15 figure
Galactic-Scale Outflows in Galaxies of the Local Universe
Galactic-scale gas outflows form a crucial ingredient in today’s galaxy evolution mod- els and are thought to regulate the gas contents - and therefore evolution - of galaxies. However, outflows are poorly understood, and thus far have been studied primarily in extreme objects rather than the normal star-forming populations. As such, several out- standing questions remain and determining the prevalence and properties of outflows in normal, star-forming galaxies, as well as their quenching potential is a prerequisite towards obtaining a complete picture of galaxy evolution. Specifically, major questions include: What is the prevalence of outflows in normal galaxies and what are their main drivers and properties? Are the properties of outflows enhanced by the presence of an AGN? What are the kpc-scale properties of outflows? Are outflows seen in all gas phases and what are their relative fractions? This Thesis aims to answers these questions by making use of the largest integrated and IFU spectroscopic data sets currently available such as the SDSS, MaNGA, xCOLD GASS, xGASS and ALFALFA surveys. Using the NaD ISM doublet and a variety of stacking techniques, we investigate the large-scale prevalence and properties of outflows in normal galaxies at z ∼0 with SDSS spectra, the kpc-scale outflow properties and their relation to galaxy properties with MaNGA IFU spectra, and finally investigate the multi- phase (i.e., molecular, neutral and ionised) nature of outflows with a stacking analysis of CO(1-0), H i 21cm, NaD and Hα tracers using the xCOLD GASS, xGASS, ALFALFA and MaNGA surveys. The Thesis finishes off with the investigation of the possible presence of a molecular gas outflow in a high redshift, lensed galaxy for which multitransitional CO and C i spectra were obtained with the IRAM 30m telescope
A spectroscopic search for AGN activity in the reionization era
The ubiquity of Lyman alpha (Ly) emission in a sample of four bright
[O III]-strong star-forming galaxies with redshifts above 7 has led to the
suggestion that such luminous sources represent a distinct population compared
to their fainter, more numerous, counterparts. The presence of Ly
emission within the reionization era could indicate that these sources created
early ionized bubbles due to their unusually strong radiation, possibly due to
the presence of active galactic nuclei. To test this hypothesis we have secured
long integration spectra with XSHOOTER on the VLT for three 7 sources
selected to have similar luminosities and prominent excess fluxes in the IRAC
3.6 or 4.5m band, usually attributed to strong [O III] emission. We
secured additional spectroscopy for one of these galaxies at =7.15 using
MOSFIRE at the Keck telescope. For this, the most well-studied source in our
sample with the strongest IRAC excess, we detect prominent nebular emission
from He II and NV indicative of a non-thermal source. For the other two sources
at =6.81 and =6.85, for which no previous optical/near infrared
spectroscopy was initially available, Ly is seen in one and CIII]
emission in the other. Although a modest sample, our results further support
the hypothesis that the phenomenon of intense [O III] emission is associated
preferentially with sources lying in early ionized bubbles. However, even
though one of our sources at =7.15 clearly indicates the presence of
non-thermal radiation, such ionized bubbles may not uniquely arise in this
manner. We discuss the unique advantages of extending such challenging
diagnostic studies with JWST.Comment: 11 pages, 7 figures, submitted to Ap
The prevalence and properties of cold gas inflows and outflows around galaxies in the local Universe
We perform a stacking analysis of the neutral Na D λλ5889, 5895 Å ISM doublet using the SDSS DR7 spectroscopic data set to probe the prevalence and characteristics of cold (T ≲ 104 K) galactic-scale gas flows in local (0.025 ≤ z ≤ 0.1) inactive and AGN-host galaxies across the SFR–M* plane. We find low-velocity outflows to be prevalent in regions of high SFRs and stellar masses (10 ≲ log M*/M⊙ ≲ 11.5), however we do not find any detections in the low-mass (log M*/M⊙ ≲ 10) regime. We also find tentative detections of inflowing gas in high-mass galaxies across the star-forming population. We derive mass outflow rates in the range of 0.14–1.74 M⊙ yr−1 and upper limits on inflow rates <1 M⊙ yr−1, allowing us to place constraints on the mass-loading factor (η = M˙out/SFR) for use in simulations of the local Universe. We discuss the fate of the outflows by comparing the force provided by the starburst to the critical force needed to push the outflow outward, and find the vast majority of the outflows unlikely to escape the host system. Finally, as outflow detection rates and central velocities do not vary strongly with the presence of a (weak) active supermassive black hole, we determine that star formation appears to be the primary driver of outflows at z ∼ 0
Newly Discovered Bright z~9-10 Galaxies and Improved Constraints on Their Prevalence Using the Full CANDELS Area
We report the results of an expanded search for z~9-10 candidates over the
~883 arcmin^2 CANDELS+ERS fields. This study adds 147 arcmin^2 to the search
area we consider over the CANDELS COSMOS, UDS, and EGS fields, while expanding
our selection to include sources with bluer J_{125}-H_{160} colors than our
previous J_{125}-H_{160}>0.5 mag selection. In searching for new z~9-10
candidates, we make full use of all available HST, Spitzer/IRAC, and
ground-based imaging data. As a result of our expanded search and use of
broader color criteria, 3 new candidate z~9-10 galaxies are identified. We also
find again the z=8.683 source previously confirmed by Zitrin+2015. This brings
our sample of probable z~9-11 galaxy candidates over the CANDELS+ERS fields to
19 sources in total, equivalent to 1 candidate per 47 arcmin^2 (1 per 10
WFC3/IR fields). To be comprehensive, we also discuss 28 mostly lower
likelihood z~9-10 candidates, including some sources that seem to be reliably
at z>8 using the HST+IRAC data alone, but which the ground-based data show are
much more likely at z<4. One case example is a bright z~9.4 candidate COS910-8
which seems instead to be at z~2. Based on this expanded sample, we obtain a
more robust LF at z~9 and improved constraints on the volume density of bright
z~9 and z~10 galaxies. Our improved z~9-10 results again reinforce previous
findings for strong evolution in the UV LF at z>8, with a factor of ~10
evolution seen in the luminosity density from z~10 to z~8.Comment: 22 pages, 12 figures, 6 tables, accepted for publication in the
Astrophysical Journa
Outflows in star-forming galaxies: Stacking analyses of resolved winds and the relation to their hosts\u27 properties
Resolving Ambiguities in the Inferred Star Formation Histories of Intense [O III] Emitters in the Reionisation Era
Early JWST spectroscopic campaigns have confirmed the presence of strong [O
III] line-emitting galaxies in the redshift interval . Although deduced
earlier from Spitzer photometry as indicative of young stellar populations,
some studies suggested the relevant photometric excesses attributed to [O III]
emission could, in part, be due to Balmer breaks arising from older stars. We
demonstrate that this is likely the case by exploiting medium-band
near-infrared JWST photometry in the Hubble Ultra Deep Field. We locate a
sample of 6 galaxies with redshifts 8.28.6 for which the relevant
medium-band filters enables us to separate the contributions of [O III]
emission and a Balmer break, thereby breaking earlier degeneracies of
interpretation. The technique is particularly valuable since it provides
photometric redshifts whose precision, , approaches
that of spectroscopic campaigns now underway with JWST. Although some sources
are young, a third of our sample have prominent Balmer breaks consistent with
stellar ages of 150 Myr. Our results indicate that even intense [O III]
emitters experienced episodes of earlier star formation to 10 and
beyond, as is now being independently deduced from direct detection of the
progenitors of similar systems.Comment: 8 pages, submitted to MNRA
Dust in the reionization era: ALMA observations of a =8.38 Galaxy
We report on the detailed analysis of a gravitationally-lensed Y-band
dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the
Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large
Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm
continuum flux suggesting the presence of dust for a star-forming galaxy with a
photometric redshift of . Deep X-SHOOTER spectra confirms the high
redshift identity of A2744_YD4 via the detection of Lyman emission at
a redshift =8.38. The association with the ALMA detection is confirmed by
the presence of [OIII] 88m emission at the same redshift. Although both
emission features are only significant at the 4 level, we argue their
joint detection and the positional coincidence with a high redshift dropout in
the HST images confirms the physical association. Analysis of the available
photometric data and the modest gravitational magnification ()
indicates A2744_YD4 has a stellar mass of 210 M, a
star formation rate of M/yr and a dust mass of
610 M. We discuss the implications of the
formation of such a dust mass only 200 Myr after the onset of cosmic
reionisation.Comment: Accepted for publication in ApJ
Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization
We report the discovery of Lyman-alpha emission (Ly) in the bright
galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at
the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was
selected for spectroscopic observations because of its photometric redshift
(), apparent brightness (H)
and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong
oxygen emission in the [4.5] band. With a total integration of 4.3 hours,
our data reveal an emission line at 11776 {\AA} which we argue is
likely Ly at a redshift , in good
agreement with the photometric estimate. The line was detected independently on
two nights using different slit orientations and its detection significance is
. An overlapping skyline contributes significantly to the
uncertainty on the total line flux although the significance of the detected
line is robust to a variety of skyline-masking procedures. By direct addition
and a Gaussian fit, we estimate a 95\% confidence range of
1.0--2.5 erg s cm, corresponding to a rest-frame
equivalent width of 17--42 {\AA}. EGSY8p7 is the most distant galaxy confirmed
spectroscopically to date, and the third luminous source in the EGS field
beyond with detectable Ly emission viewed at a
time when the intergalactic medium is believed to be fairly neutral. Although
the reionization process was probably patchy, we discuss whether luminous
sources with prominent IRAC color excesses may harbor harder ionizing spectra
than the dominant fainter population thereby creating earlier ionized bubbles.
Further spectroscopic follow-up of such bright sources promises important
insight into the early formation of galaxies.Comment: V3: ApJL accepted; 7 pages, 4 figures, 1 tabl
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