129 research outputs found
The [OIII] equivalent width distribution at z : The redshift evolution of the extreme emission line galaxies
We determine the [OIII] equivalent width (EW) distribution of
rest-frame UV-selected (M) star-forming
galaxies in the GOODS North and South fields. We make use of deep HDUV
broadband photometry catalogues for selection and 3D-HST WFC3/IR grism spectra
for measurement of line properties. The [OIII] EW distribution
allows us to measure the abundance of extreme emission line galaxies (EELGs)
within this population. We model a log-normal distribution to the
[OIII] rest-frame equivalent widths of galaxies in our sample,
with location parameter and variance parameter . This EW distribution has a mean [OIII] EW of
168. The fractions of rest-UV-selected galaxies with
[OIII] EWs greater than and are measured to
be , , and
respectively. The EELG fractions do not vary strongly with UV luminosity in the
range () considered in this paper, consistent with
findings at higher redshifts. We compare our results to and
studies where candidate EELGs have been discovered through
Spitzer/IRAC colours, and we identify rapid evolution with redshift in the
fraction of star-forming galaxies observed in an extreme emission line phase (a
rise by a factor between and ). This
evolution is consistent with an increased incidence of strong bursts in the
galaxy population of the reionisation era. While this population makes a
sub-dominant contribution of the ionising emissivity at , EELGs
are likely to dominate the ionising output in the reionisation era.Comment: Submitted to MNRAS. 13 pages, 6 figure
The Number Density Evolution of Extreme Emission Line Galaxies in 3D-HST: Results from a Novel Automated Line Search Technique for Slitless Spectroscopy
The multiplexing capability of slitless spectroscopy is a powerful asset in
creating large spectroscopic datasets, but issues such as spectral confusion
make the interpretation of the data challenging. Here we present a new method
to search for emission lines in the slitless spectroscopic data from the 3D-HST
survey utilizing the Wide-Field Camera 3 on board the Hubble Space Telescope.
Using a novel statistical technique, we can detect compact (extended) emission
lines at 90% completeness down to fluxes of 1.5 (3.0) times 10^{-17}
erg/s/cm^2, close to the noise level of the grism exposures, for objects
detected in the deep ancillary photometric data. Unlike previous methods, the
Bayesian nature allows for probabilistic line identifications, namely redshift
estimates, based on secondary emission line detections and/or photometric
redshift priors. As a first application, we measure the comoving number density
of Extreme Emission Line Galaxies (restframe [O III] 5007 equivalent widths in
excess of 500 Angstroms). We find that these galaxies are nearly 10 times more
common above z~1.5 than at z<0.5. With upcoming large grism surveys such as
Euclid and WFIRST as well as grisms featuring prominently on the NIRISS and
NIRCam instruments on James Webb Space Telescope, methods like the one
presented here will be crucial for constructing emission line redshift catalogs
in an automated and well-understood manner.Comment: 16 pages, 14 Figures; Accepted to Ap
An Absence of Radio-Loud Active Galactic Nuclei in Geometrically Flat Quiescent Galaxies: Implications for Maintenance-Mode Feedback Models
Maintenance-mode feedback from low-accretion rate AGN, manifesting itself
observationally through radio-loudness, is invoked in all cosmological galaxy
formation models as a mechanism that prevents excessive star-formation in
massive galaxies (M 310 M). We
demonstrate that at a fixed mass the incidence of radio-loud AGN (L
10 WHz) identified in the FIRST and NVSS radio surveys among a
large sample of quiescent (non-star forming) galaxies selected from the SDSS is
much higher in geometrically round galaxies than in geometrically flat,
disk-like galaxies. As found previously, the RL AGN fraction increases steeply
with stellar velocity dispersion and stellar mass, but even at a
fixed velocity dispersion of 200-250 kms this fraction increases from
0.3% for flat galaxies (projected axis ratio of q 0.4) to 5% for round
galaxies (q 0.8). We rule out that this strong trend is due to projection
effects in the measured velocity dispersion. The large fraction of radio-loud
AGN in massive, round galaxies is consistent with the hypothesis that such AGN
deposit energy into their hot gaseous halos, preventing cooling and
star-formation. However, the absence of such AGN in disk-like quiescent
galaxies -- most of which are not satellites in massive clusters, raises
important questions: is maintenance-mode feedback a generally valid explanation
for quiescence; and, if so, how does that feedback avoid manifesting at least
occasionally as a radio-loud galaxy?Comment: 7 pages, 5 figures, accepted for publication in ApJ Letter
Stars, gas, and star formation of distant post-starburst galaxies
We present a comprehensive multi-wavelength study of 5 poststarburst galaxies
with at , examining their stars, gas, and
current and past star-formation activities. Using optical images from the
Subaru telescope and Hubble Space Telescope, we observe a high incidence of
companion galaxies and low surface brightness tidal features, indicating that
quenching is closely related to interactions between galaxies. From optical
spectra provided by the LEGA-C survey, we model the stellar continuum to derive
the star-formation histories and show that the stellar masses of progenitors
ranging from to , undergoing a burst of
star formation several hundred million years prior to observation, with a decay
time scale of million years. Our ALMA observations detect CO(2-1)
emission in four galaxies, with the molecular gas spreading over up to ,
or kpc, with a mass of up to . However,
star-forming regions are unresolved by either the slit spectra or 3~GHz
continuum observed by the Very Large Array. Comparisons between the
star-formation rates and gas masses, and the sizes of CO emission and
star-forming regions suggest a low star-forming efficiency. We show that the
star-formation rates derived from IR and radio luminosities with commonly-used
calibrations tend to overestimate the true values because of the prodigious
amount of radiation from old stars and the contribution from AGN, as the
optical spectra reveal weak AGN-driven outflows.Comment: Accepted by Ap
Recommended from our members
MUSE crowded field 3D spectroscopy in NGC 300: III. Characterizing extremely faint HII regions and diffuse ionized gas
Context. There are known differences between the physical properties of H II and diffuse ionized gas (DIG). However, most of the studied regions in the literature are relatively bright, with log10 L(Hα)[erg s-1] ≳37. Aims. We compiled an extremely faint sample of 390 H II regions with a median Hα luminosity of 34.7 in the flocculent spiral galaxy NGC 300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. Methods. We used MUSE data of nine fields in NGC 300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. We binned the data in dendrogram leaves and extracted all strong nebular emission lines. We identified H II and DIG regions and compared their electron densities, metallicity, extinction, and kinematic properties. We also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the H II and DIG regions. Results. The gas density in the H II and DIG regions is close to the low-density limit in all fields. The average velocity dispersion in the DIG is higher than in the H II regions, which can be explained by the DIG being 1.8 kK hotter than H II gas. The DIG manifests a lower ionization parameter than H II gas, and the DIG fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the DIG ionization. Most of the DIG is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the H II gas. We observe a flat metallicity profile in the central region of NGC 300, without a sign of a gradient. Conclusions. The differences between extremely faint H II and DIG regions follow the same trends and correlations as their much brighter cousins. Both types of objects are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes
MUSE crowded field 3D spectroscopy in NGC 300 III. Characterizing extremely faint HII regions and diffuse ionized gas
There are known differences between the physical properties of HII and
diffuse ionized gas (DIG), but most of the studied regions in the literature
are relatively bright. We compiled a faint sample of 390 HII regions with
median =34.7 in the spiral galaxy NGC300, derived their
physical properties in terms of metallicity, density, extinction, and
kinematics, and performed a comparative analysis of the properties of the DIG.
We used MUSE data of nine fields in NGC300, covering a galactocentric distance
of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm
regions. We binned the data in dendrogram leaves and extracted all strong
nebular emission lines. We identified HII and DIG regions and compared their
electron densities, metallicity, extinction, and kinematic properties. We also
tested the effectiveness of unsupervised machine-learning algorithms in
distinguishing between the HII and DIG regions. The gas density in the HII and
DIG regions is close to the low-density limit in all fields. The average
velocity dispersion in the DIG is higher than in the HII regions, which can be
explained by the DIG being 1.8 kK hotter than HII gas. The DIG manifests a
lower ionization parameter than HII gas, and the DIG fractions vary between
15-77%, with strong evidence of a contribution by hot low-mass evolved stars
and shocks to the DIG ionization. Most of the DIG is consistent with no
extinction and an oxygen metallicity that is indistinguishable from that of the
HII gas.We observe a flat metallicity profile in the central region, without a
sign of a gradient. The differences between extremely faint HII and DIG regions
follow the same trends and correlations as their much brighter cousins. HII and
DIG are so heterogeneous, however, that the differences within each class are
larger than the differences between the two classes.Comment: Accepted in A&
The Spatial Extent and Distribution of Star Formation in 3D-HST Mergers at z~1.5
We present an analysis of the spatial distribution of star formation in a
sample of 60 visually identified galaxy merger candidates at z>1. Our sample,
drawn from the 3D-HST survey, is flux-limited and was selected to have high
star formation rates based on fits of their broad-band, low spatial resolution
spectral energy distributions. It includes plausible pre-merger (close pairs)
and post-merger (single objects with tidal features) systems, with total
stellar masses and star formation rates derived from multi-wavelength
photometry. Here we use near-infrared slitless spectra from 3D-HST which
produce Halpha or [OIII] emission line maps as proxies for star-formation maps.
This provides a first comprehensive high-resolution, empirical picture of where
star formation occurred in galaxy mergers at the epoch of peak cosmic star
formation rate. We find that detectable star formation can occur in one or both
galaxy centres, or in tidal tails. The most common case (58%) is that star
formation is largely concentrated in a single, compact region, coincident with
the centre of (one of) the merger components. No correlations between star
formation morphology and redshift, total stellar mass, or star formation rate
are found. A restricted set of hydrodynamical merger simulations between
similarly massive and gas-rich objects implies that star formation should be
detectable in both merger components, when the gas fractions of the individual
components are the same. This suggests that z~1.5 mergers typically occur
between galaxies whose gas fractions, masses, and/or star formation rates are
distinctly different from one another.Comment: Accepted for publication in MNRAS, 16 pages, 10 figure
Large-scale excess HI absorption around galaxies detected in a background galaxy spectrum in the MUSE eXtremely Deep Field
Observationally mapping the relation between galaxies and the intergalactic
medium (IGM) is of key interest for studies of cosmic reionization. Diffuse
hydrogen gas has typically been observed in HI Lyman- (Ly)
absorption in the spectra of bright background quasars. However, it is
important to extend these measurements to background galaxies as quasars become
increasingly rare at high redshift and rarely probe closely separated
sight-lines. Here we use deep integral field spectroscopy in the MUSE eXtremely
Deep Field to demonstrate the measurement of the Ly transmission at
in absorption to a background galaxy at . The HI
transmission is consistent with independent quasar sight-lines at similar
redshifts. Exploiting the high number of spectroscopic redshifts of faint
galaxies (500 between within a radius of 8 arcmin) that are tracers
of the density field, we show that Ly transmission is inversely
correlated with galaxy density, i.e. transparent regions in the Ly
forest mark under-dense regions at . Due to large-scale clustering,
galaxies are surrounded by excess HI absorption over the cosmic mean out to 4
cMpc/h. We also find that redshifts from the peak of the Ly line are
typically offset from the systemic redshift by +170 km/s. This work extends
results from to higher redshifts and demonstrates the power of
deep integral field spectroscopy to simultaneously measure the ionization
structure of the IGM and the large-scale density field in the early Universe.Comment: Submitted to MNRAS. Main text 9 pages, 9 figures. Key results in Fig
4 (Lya forest transmission in the MXDF field) and Fig 9 (transmission -
galaxy distance cross-correlation
The first comprehensive study of a giant nebula around a radio-quiet quasar in the Universe
We present the first comprehensive study of a giant,
kpc-scale nebula around a radio-quiet quasar at . The analysis is based on
deep integral field spectroscopy with MUSE of the field of HE02381904, a
luminous quasar at . The nebula emits strongly in , , and , and the quasar resides in an
unusually overdense environment for a radio-quiet system. The environment
likely consists of two groups which may be merging, and in total have an
estimated dynamical mass of to $10^{14}\
{\rm M_\odot}\mathrm{[O \, II]}\log(n_{\rm e, \, [O \, II]} / \mathrm{cm^{-3}}) < 1.22.8\mathrm{[O\,II]}\mathrm{[O\,III]}\mathrm{[Ne\,V]}10{-}400\approx
10^4{-}10^5$ years.Comment: 19 pages, 9 figures, 3 tables; Submitted to MNRA
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