We present a comprehensive study of the physical properties of ∼ 10 5 galaxies with measurable star formation in the Sloan Digital Sky Survey (SDSS). By comparing physical information extracted from the emission lines with continuum properties, we build up a picture of the nature of star-forming galaxies at z < 0.2. We develop a method for aperture correction using resolved imaging and show that our method takes out essentially all aperture bias in the star formation rate (SFR) estimates, allowing an accurate estimate of the total SFRs in galaxies. We determine the SFR density to be 1.915 +0.02 −0.01 (random) +0.14

The physical properties of star-forming galaxies in the low-redshift universe

The Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, from z approx. 8 - 1.5. It will image > 250,000 distant galaxies using three separate cameras on the Hubble Space Tele8cope, from the mid-UV to near-IR, and will find and measure Type Ia supernovae beyond z > 1.5 to test their accuracy as standard candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10(exp 9) solar mass to z approx. 2, reaching the knee of the UV luminosity function of galaxies to z approx. 8. The survey covers approximately 800 square arc minutes and is divided into two parts. The CANDELS/Deep survey (5(sigma) point-source limit H =27.7mag) covers approx. 125 square arcminutes within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (EGS, COSMOS, and UDS) and covers the full area to a 50(sigma) point-source limit of H ? or approx. = 27.0 mag. Together with the Hubble Ultradeep Fields, the strategy creates a three-tiered "wedding cake" approach that has proven efficient for extragalactic surveys. Data from the survey are non-proprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design.

/pdf/candels-the-cosmic-assembly-near-infrared-deep-extragalactic-4x4epz7mkw.pdf

CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey

We develop a method for interpreting faint galaxy data which focuses on the integrated light radiated from the galaxy population as a whole. The emission history of the universe at ultraviolet, optical, and near-infrared wavelengths is modeled from the present epoch to z ≈ 4 by tracing the evolution with cosmic time of the galaxy luminosity density, as determined from several deep spectroscopic samples and the Hubble Deep Field (HDF) imaging survey. In a q0 = 0.5, h50 = 1 cosmology, the global spectrophotometric properties of field galaxies can be well fitted by a simple stellar evolution model, defined by a time-dependent star formation rate (SFR) per unit comoving volume and a universal initial mass function (IMF) extending from 0.1 to 125 M☉. While a Salpeter IMF with a modest amount of dust reddening or a somewhat steeper mass function, (m) m-2.7, can both reproduce the data reasonably well, a Scalo IMF produces too much long-wavelength light and is unable to match the observed mean galaxy colors. In the best-fit models, the global SFR rises sharply, by about an order of magnitude, from a redshift of zero to a peak value at z ≈ 1.5 in the range 0.12-0.17 M☉ yr-1 Mpc-3, to fall again at higher redshifts. After integrating the inferred star formation rate over cosmic time, we find a stellar mass density at the present epoch of Ω -->s h -->2500.005, hence a mean stellar mass-to-light ratio 4 in the B-band and 1 in K, consistent with the values observed in nearby galaxies of various morphological types. The models are able to account for the entire background light recorded in the galaxy counts down to the very faint magnitude levels probed by the HDF. Since only ~20% of the current stellar content of galaxies is produced at z > 2, a rather low cosmic metallicity is expected at these early times, in good agreement with the observed enrichment history of the damped Lyα systems. The biggest uncertainty is represented by the poorly constrained amount of starlight that was absorbed by dust and reradiated in the IR at early epochs. A monolithic collapse model, where half of the present-day stars formed at z > 2.5 and were shrouded by dust, can be made consistent with the global history of light, but overpredicts the metal mass density at high redshifts as sampled by quasi-stellar object absorbers.

https://iopscience.iop.org/article/10.1086/305523/pdf

The Star formation history of field galaxies

A new stellar library developed for stellar population synthesis modelling is presented. The library consists of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained at the 2.5-m Isaac Newton Telescope and cover the range λλ 3525–7500 A at 2.3 A (full width at half-maximum) spectral resolution. The spectral resolution, spectral-type coverage, flux-calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population-synthesis models.

https://eprints.ucm.es/29321/1/cardiel42libre.pdf

Medium-resolution isaac newton telescope library of empirical spectra

In the local Universe, most galaxies are dominated by stars, with less than ten per cent of their visible mass in the form of gas. Determining when most of these stars formed is one of the central issues of observational cosmology. Optical and ultraviolet observations of high-redshift galaxies (particularly those in the Hubble Deep Field) have been interpreted as indicating that the peak of star formation occurred between redshifts of 1 and 1.5. But it is known that star formation takes place in dense clouds, and is often hidden at optical wavelengths because of extinction by dust in the clouds. Here we report a deep submillimetre-wavelength survey of the Hubble Deep Field; these wavelengths trace directly the emission from dust that has been warmed by massive star-formation activity. The combined radiation of the five most significant detections accounts for 30–50 per cent of the previously unresolved background emission in this area. Four of these sources appear to be galaxies in the redshift range 2< z < 4, which, assuming these objects have properties comparable to local dust-enshrouded starburst galaxies, implies a star-formation rate during that period about a factor of five higher than that inferred from the optical and ultraviolet observations.

/pdf/high-redshift-star-formation-in-the-hubble-deep-field-wez72o79f2.pdf

High-redshift star formation in the Hubble Deep Field revealed by a submillimetre-wavelength survey

The Universidad Complutense de Madrid (UCM) survey is a long-term project aimed at finding and analyzing star-forming galaxies detected by their Hα emission in Schmidt objective-prism plates The instrumental setup limits the volume of the universe surveyed to a redshift z ≲ 0045 So far we have discovered several hundred emission-line galaxies (ELGs) undergoing star formation at a wide range of levels Analyzing a complete sample of ELGs from the UCM survey, we have computed the Hα luminosity function for the star-forming galaxies in the surveyed volume of the universe A Schechter function provides a good fit to the H_α luminosity function with the following parameters: α = -13 ± 02, L^*(H_α) = 10^4215±008 ergs s^-1, and φ^* = 10^-32±02 Mpc^3 for H_0 = 50 km s^-1 Mpc^-1 Integrating over the full range of luminosities, we obtain an H_α luminosity density of 10^391±02 ergs s^-1 Mpc^-3 Using the H_α emission as a star formation rate (SFR) estimator, this translates into a SFR density for the local universe of 0013_−0005^+0007 M_☉ yr^-1 Mpc^-3 in star-forming galaxies with EW(H_α + [N_II]) > 10 A and z lesssim 0045 for a Scalo initial mass function This is the first observational determination of this quantity, which will provide a direct test of current galaxy formation and evolution models

/pdf/the-current-star-formation-rate-of-the-local-universe-43op0axkjw.pdf

The Current Star Formation Rate of the Local Universe

Spectroscopic observations for the full sample of Her emission-line galaxy candidates (ELGs) from the Universidad Complutense de Madrid objective-prism survey Lists 1 and 2 have been obtained in order to investigate fully the properties of the survey constituents as well as the selection characteristics and completeness limits of the survey itself. The spectroscopic data include redshifts, line fluxes, equivalent widths, emission-line ratios, optical reddening estimates and synthesized color indexes. We find that 74% of the objects in this sample do exhibit emission Lines. We compare our observational data, with parameters given in the published survey lists in order to assess the usefulness of the latter. The different emission-line galaxies have been classified according to their spectra in several groups. Gray-scale images of the CCD spectra near the main emission lines, spatial profiles at the continuum and the Line for [OIII] λ5007 and Hα lines, as well as plots of the coadded spectra of selected galaxies are presented, and a number of peculiar objects are described.

/pdf/observations-of-a-complete-sample-of-ha-emission-line-3inbm6zxf1.pdf

Observations of a complete sample of Hα emission-line galaxies. Long-slit spectroscopy of galaxies in UCM lists 1 and 2.

A spectroscopic analysis of the entire sample of Ha emission-line galaxies (ELGs) contained in lists 1 and 2 of the Universidad Complutense de Madrid (UCM) objective-prism survey is presented. A significant fraction (59%) of star-forming galaxies with low-ionization or high-extinction properties has been found. This kind of ELG is only incompletely detected in the blue or in other ELG surveys. We have found evidence for evolution among some of the different ELG classes. A comparison between the populations detected by the Case, Kiso, University of Michigan, and UCM surveys is presented. We conclude that a deep H_α survey is better able to sample all the ages, evolutionary stages, and luminosities of currently star-forming galaxies than other surveys using blue emission lines or colors. Finally, the luminosity and spatial distributions of the UCM galaxies are determined. The contribution of the newly found, currently star-forming ELGs provides new clues to galaxy evolution and has to be taken into account when trying to consider the density of ELGs and total star formation rate in the universe.

/pdf/spectroscopic-properties-and-luminosity-distribution-of-the-561soh2vdy.pdf

Spectroscopic Properties and Luminosity Distribution of the Universidad Complutense de Madrid Survey Galaxies

/pdf/the-o-csc-ii-csc-l3727-luminosity-function-of-the-local-5c8mjboer2.pdf

The [O [CSC]ii[/CSC]] λ3727 Luminosity Function of the Local Universe

The measurement of the Star Formation Rate density of the Universe is of prime importance in understanding the formation and evolution of galaxies. The [OII]3727 emission line flux, easy to measure up to z~1.4 within deep redshift surveys in the optical and up to z~5.4 in the near infrared, offers a reliable means of characterizing the star formation properties of high-z objects. In order to provide the high-z studies with a local reference, we have measured total [OII]3727 fluxes for the well analyzed local sample of star-forming galaxies from the Universidad Complutense de Madrid Survey. This data is used to derive the [OII]3727 luminosity function for local star-forming galaxies. When compared with similar luminosity densities published for redshift up to z~1, the overall evolution already observed in the star formation activity of the Universe is confirmed.

/pdf/the-oii-3727-luminosity-function-of-the-local-universe-2tfahe5omh.pdf

M. Rego

Papers

The Current Star Formation Rate of the Local Universe

Observations of a complete sample of Hα emission-line galaxies. Long-slit spectroscopy of galaxies in UCM lists 1 and 2.

Spectroscopic Properties and Luminosity Distribution of the Universidad Complutense de Madrid Survey Galaxies

The [O [CSC]ii[/CSC]] λ3727 Luminosity Function of the Local Universe

The [OII]3727 Luminosity Function of the Local Universe