2018A&A...612A..94N


Query : 2018A&A...612A..94N

2018A&A...612A..94N - Astronomy and Astrophysics, volume 612A, 94-94 (2018/4-1)

The VIMOS Ultra Deep Survey: Nature, ISM properties, and ionizing spectra of CIII]λ1909 emitters at z = 2-4.

NAKAJIMA K., SCHAERER D., LE FEVRE O., AMORIN R., TALIA M., LEMAUX B.C., TASCA L.A.M., VANZELLA E., ZAMORANI G., BARDELLI S., GRAZIAN A., GUAITA L., HATHI N.P., PENTERICCI L. and ZUCCA E.

Abstract (from CDS):


Context. Ultraviolet (UV) emission-line spectra are used to spectroscopically confirm high-z galaxies and increasingly also to determine their physical properties.
Aims. We construct photoionization models to interpret the observed UV spectra of distant galaxies in terms of the dominant radiation field and the physical condition of the interstellar medium (ISM). These models are applied to new spectroscopic observations from the VIMOS Ultra Deep Survey (VUDS).
Methods. We construct a large grid of photoionization models, which use several incident radiation fields (stellar populations, active galactic nuclei (AGNs), mix of stars and AGNs, blackbodies, and others), and cover a wide range of metallicities and ionization parameters. From these models we derive new spectral UV line diagnostics using equivalent widths (EWs) of [CIII]λ1909 doublet, CIVλ1549 doublet and the line ratios of [CIII], CIV, and HeIIλ1640 recombination lines. We apply these diagnostics to a sample of 450 [CIII]-emitting galaxies at redshifts z=2-4 previously identified in VUDS.
Results. We demonstrate that our photoionization models successfully reproduce observations of nearby and high-redshift sources with known radiation field and/or metallicity. For star-forming galaxies our models predict that [CIII] EW peaks at sub-solar metallicities, whereas CIV EW peaks at even lower metallicity. Using the UV diagnostics, we show that the average star-forming galaxy (EW([CIII])∼2Å) based on the composite of the 450 UV-selected galaxies' spectra The inferred metallicity and ionization parameter is typically Z=0.3-0.5Z and logU=-2.7 to - 3, in agreement with earlier works at similar redshifts. The models also indicate an average age of 50-200Myr since the beginning of the current star-formation, and an ionizing photon production rate, ξion, of logξion/erg–1Hz = 25.3-25.4. Among the sources with EW([CIII])≥10Å, approximately 30% are likely dominated by AGNs. The metallicity derived for galaxies with EW(CIII)=10-20Å is low, Z=0.02-0.2Z, and the ionization parameter higher (logU~-1.7) than the average star-forming galaxy. To explain the average UV observations of the strongest but rarest [CIII] emitters (EW([CIII])>20Å), we find that stellar photoionization is clearly insufficient. A radiation field consisting of a mix of a young stellar population (logξion/erg–1Hz∼25.7) plus an AGN component is required. Furthermore an enhanced C/O abundance ratio (up to the solar value) is needed for metallicities Z=0.1-0.2Z and logU=-1.7 to - 1.5.
Conclusions. A large grid of photoionization models has allowed us to propose new diagnostic diagrams to classify the nature of the ionizing radiation field (star formation or AGN) of distant galaxies using UV emission lines, and to constrain their ISM properties. We have applied this grid to a sample of [CIII]-emitting galaxies at z=2-4 detected in VUDS, finding a range of physical properties and clear evidence for significant AGN contribution in rare sources with very strong [CIII] emission. The UV diagnostics we propose should also serve as an important basis for the interpretation of upcoming observations of high-redshift galaxies.

Abstract Copyright: © ESO 2018

Journal keyword(s): galaxies: abundances - galaxies: evolution - galaxies: high-redshift - galaxies: ISM

Simbad objects: 3

goto Full paper

goto View the references in ADS

Number of rows : 3
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 [ZFM2015] A383 5.2 LeG 02 48 04.600 -03 31 58.47         26.2 ~ 19 1
2 NAME Lynx Arc LeI 08 48 48.76 +44 55 48.6           ~ 43 0
3 NAME EGS-zs8-1 G 14 20 34.893 +53 00 15.33           ~ 34 0

To bookmark this query, right click on this link: simbad:objects in 2018A&A...612A..94N and select 'bookmark this link' or equivalent in the popup menu