10 research outputs found
The evolution of the equivalent width of the Hα emission line and specific star formation rate in star-forming galaxies at 1 < z < 5
We present the results of a study which uses spectral energy distribution
(SED) fitting to investigate the evolution of the equivalent width (EW) of the
Halpha emission line in star-forming galaxies over the redshift interval 1<z<5.
After first demonstrating the ability of our SED-fitting technique to recover
EW(Ha) using a sample of galaxies at z~1.3 with EW(Ha) measurements from 3D-HST
grism spectroscopy, we proceed to apply our technique to samples of
spectroscopically confirmed and photometric-redshift selected star-forming
galaxies at z>=1 in the CANDELS UDS and GOODS-S fields. Confining our analysis
to a constant stellar mass range (9.5<log(M/Msun)<10.5), we find that the
median EW(Ha) evolves only modestly with redshift, reaching a rest-frame value
of EW(Ha)=301+/-30 Angs by redshift z~4.5. Furthermore, using estimates of
star-formation rate (SFR) based on both UV luminosity and Ha line flux, we use
our galaxy samples to compare the evolution of EW(Ha) and specific
star-formation rate (sSFR). Our results indicate that over the redshift range
1<z<5, the evolution displayed by EW(Ha) and sSFR is consistent, and can be
adequately parameterized as: propto (1+z)^(1.0+/-0.2). As a consequence, over
this redshift range we find that the sSFR and rest-frame EW(Ha) of star-forming
galaxies with stellar masses M~10^(10) Msun are related by:
EW(Ha)/Ang=(63+/-7)sSFR/Gyr^(-1). Given the current uncertainties in measuring
the SFRs of high-redshift galaxies, we conclude that EW(Ha) provides a useful
independent tracer of sSFR for star-forming galaxies out to redshifts of z=5.Comment: Version accepted to publication in MNRAS, 11 pages, 5 figures, 1
tabl
The effects of spatial resolution on Integral Field Spectrograph surveys at different redshifts. The CALIFA perspective
Over the past decade, 3D optical spectroscopy has become the preferred tool
for understanding the properties of galaxies and is now increasingly used to
carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass,
ATLAS3D, PINGS and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS,
GLACE, and IMAGES have targeted the most luminous galaxies to study mainly
their kinematic properties. The on-going CALIFA survey () is the
first of a series of upcoming Integral Field Spectroscopy (IFS) surveys with
large samples representative of the entire population of galaxies. Others
include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at
higher redshift. Given the importance of spatial scales in IFS surveys, the
study of the effects of spatial resolution on the recovered parameters becomes
important. We explore the capability of the CALIFA survey and a hypothetical
higher redshift survey to reproduce the properties of a sample of objects
observed with better spatial resolution at lower redshift. Using a sample of
PINGS galaxies, we simulate observations at different redshifts. We then study
the behaviour of different parameters as the spatial resolution degrades with
increasing redshift.Comment: 20 pages, 16 figures. Accepted for publication in A&
CALIFA, the Calar Alto Legacy Integral Field Area survey: I. Survey presentation
We present here the Calar Alto Legacy Integral Field Area (CALIFA) survey,
which has been designed to provide a first step in this direction.We summarize
the survey goals and design, including sample selection and observational
strategy.We also showcase the data taken during the first observing runs
(June/July 2010) and outline the reduction pipeline, quality control schemes
and general characteristics of the reduced data. This survey is obtaining
spatially resolved spectroscopic information of a diameter selected sample of
galaxies in the Local Universe (0.005< z <0.03). CALIFA has been
designed to allow the building of two-dimensional maps of the following
quantities: (a) stellar populations: ages and metallicities; (b) ionized gas:
distribution, excitation mechanism and chemical abundances; and (c) kinematic
properties: both from stellar and ionized gas components. CALIFA uses the PPAK
Integral Field Unit (IFU), with a hexagonal field-of-view of
\sim1.3\sq\arcmin', with a 100% covering factor by adopting a three-pointing
dithering scheme. The optical wavelength range is covered from 3700 to 7000
{\AA}, using two overlapping setups (V500 and V1200), with different
resolutions: R\sim850 and R\sim1650, respectively. CALIFA is a legacy survey,
intended for the community. The reduced data will be released, once the quality
has been guaranteed. The analyzed data fulfill the expectations of the original
observing proposal, on the basis of a set of quality checks and exploratory
analysis.
We conclude from this first look at the data that CALIFA will be an important
resource for archaeological studies of galaxies in the Local Universe.Comment: 32 pages, 29 figures, Accepted for publishing in Astronomy and
Astrophysic
The VANDELS ESO public spectroscopic survey: Observations and first data release
This paper describes the observations and the first data release (DR1) of the ESO public spectroscopic survey âVANDELS, a deep VIMOS survey of the CANDELS CDFS and UDS fieldsâ. The main targets of VANDELS are star-forming galaxies at redshift 2.4 < z < 5.5, an epoch when the Universe had not yet reached 20% of its current age, and massive passive galaxies in the range 1 < z < 2.5. By adopting a strategy of ultra-long exposure times, ranging from a minimum of 20 h to a maximum of 80 h per source, VANDELS is specifically designed to be the deepest-ever spectroscopic survey of the high-redshift Universe. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the survey is obtaining ultra-deep optical spectroscopy covering the wavelength range 4800â10 000 â« with a sufficiently high signal-to-noise ratio to investigate the astrophysics of high-redshift galaxy evolution via detailed absorption line studies of well-defined samples of high-redshift galaxies. VANDELS-DR1 is the release of all medium-resolution spectroscopic data obtained during the first season of observations, on a 0.2 square degree area centered around the CANDELS-CDFS (Chandra deep-field south) and CANDELS-UDS (ultra-deep survey) areas. It includes data for all galaxies for which the total (or half of the total) scheduled integration time was completed. The DR1 contains 879 individual objects, approximately half in each of the two fields, that have a measured redshift, with the highest reliable redshifts reaching zspec ~ 6. In DR1 we include fully wavelength-calibrated and flux-calibrated 1D spectra, the associated error spectrum and sky spectrum, and the associated wavelength-calibrated 2D spectra. We also provide a catalog with the essential galaxy parameters, including spectroscopic redshifts and redshift quality flags measured by the collaboration. We present the survey layout and observations, the data reduction and redshift measurement procedure, and the general properties of the VANDELS-DR1 sample. In particular, we discuss the spectroscopic redshift distribution and the accuracy of the photometricredshifts for each individual target category, and we provide some examples of data products for the various target typesand the different quality flags. All VANDELS-DR1 data are publicly available and can be retrieved from the ESO archive. Two further data releases are foreseen in the next two years, and a final data release is currently scheduled for June 2020, which will include an improved rereduction of the entire spectroscopic data set
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest frame properties in Abell-2744 and MACS-J0416
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to cluster members themselves. Methods. We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC, which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six different approaches to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts. Results. We show that photometric redshifts reach a remarkable similar to 3-5% accuracy. After accounting for magnification, the H-band number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending the presently available samples to galaxies that, intrinsically, are as faint as H similar to 32-33, thanks to strong gravitational lensing. The Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5-1.5 dex lower masses with respect to extragalactic wide fields, including sources at M-star similar to 10(7)-10(8) M-circle dot at z > 5. Similarly, they allow the detection of objects with intrinsic star formation rates (SFRs) > 1 dex lower than in the CANDELS fields reaching 0.1-1 M-circle dot/yr at z similar to 6-10
THE LYMAN-CONTINUUM PHOTON PRODUCTION EFFICIENCY Ο
Galaxies represent one of the preferred candidate sources to drive the
reionization of the universe. Even as gains are made in mapping the galaxy UV
luminosity density to z>6, significant uncertainties remain regarding the
conversion to the implied ionizing emissivity. The relevant unknowns are the
Lyman-continuum (LyC) photon production efficiency xi_{ion} and the escape
fraction f_{esc}. As we show here, the first of these unknowns is directly
measureable in z=4-5 galaxies, based on the impact the Halpha line has on the
observed IRAC fluxes. By computing a LyC photon production rate from the
implied Halpha luminosities for a broad selection of z=4-5 galaxies and
comparing this against the dust-corrected UV-continuum luminosities, we provide
the first-ever direct estimates of the LyC photon production efficiency
xi_{ion} for the z>~4 galaxy population. We find log_{10} xi_{ion}/[Hz/ergs] to
have a mean value of 25.27_{-0.03}^{+0.03} and 25.34_{-0.02}^{+0.02} for sub-L*
z=4-5 galaxies adopting Calzetti and SMC dust laws, respectively. Reassuringly,
both values are consistent with standardly assumed xi_{ion}'s in reionization
models, with a slight preference for higher xi_{ion}'s (by ~0.1 dex) adopting
the SMC dust law. A modest ~0.03-dex increase in these estimates would result
if the escape fraction for ionizing photons is non-zero and galaxies dominate
the ionizing emissivity at z~4.4. High values of xi_{ion} (~25.5-25.8 dex) are
derived for the bluest galaxies (beta<-2.3) in our samples, independent of dust
law and consistent with results for a z=7.045 galaxy. Such elevated values of
xi_{ion} would have important consequences, indicating that f_{esc} cannot be
in excess of 13% unless the galaxy UV luminosity function does not extend down
to -13 mag or the clumping factor is greater than 3. A low escape fraction
would fit well with the low rate of LyC leakage observed at z~3.Comment: 12 pages, 6 figures, 3 tables, updated to match the version in press,
both statistical and systematic errors given for xi_{ion