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تسجيل مستخدم جديدThe physical properties and evolution of Lyalpha emitting galaxies
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A significant fraction of high redshift starburst galaxies presents strong Ly alpha emission. Understanding the nature of these galaxies is important to assess the role they played in the early Universe and to shed light on the relation between the narrow band selected Lyalpha emitters and the Lyman break galaxies: are the Lyalpha emitters a subset of the general LBG population? or do they represent the youngest galaxies in their early phases of formation? We studied a sample of UV continuum selected galaxies from z~2.5 to z~6 (U, B, V and i-dropouts) from the GOODS-South survey, that have been observed spectroscopically. Using the GOODS-MUSIC catalog we investigated their physical properties, such as total masses, ages, SFRs, extinction etc as determined from a spectrophotometric fit to the multi-wavelength (U band to mid-IR) SEDs, and their dependence on the emission line characteristics. In particular we determined the nature of the LBGs with Lyalpha in emission and compared them to the properties of narrow band selected Lyalpha emitters. For U and B-dropouts we also compared the properties of LBGs with and without the Lyalpha emission line.
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We have analyzed a sample of LBGs from z =3.5 to z=6 selected from the GOODS-S field as B,V and i-dropouts, and with spectroscopic observations showing that they have the Lyalpha line in emission. Our main aim is to investigate their physical propert
ies and their dependence on the emission line characteristics, to shed light on the relation between galaxies with Lyalpha emission and the general LBG population.The objects were selected from their continuum colors and then spectroscopically confirmed by the GOODS collaboration and other campaigns. From the spectra we derived the line flux and EW. We then used U-band to mid-IR photometry from GOODS-MUSIC to derive the physical properties of the galaxies, such as total stellar mass, age and so on, through standard SED fitting techniques.Although most galaxies are fit by young stellar populations, a small but non negligible fraction has SEDs that require considerably older stellar component, up to 1 Gyr. There is no apparent relation between age and EW: some of the oldest galaxies have large EW, and should be also selected in narrow band surveys. Therefore not all Lyalpha emitters are primeval galaxies in the very early stages of formation,as is commonly assumed. We also find a large range of stellar populations, with masses from 5x10^8 Msol to 5x10^10 Msol and SFR from few to 60 Msol/yr. Although there is no correlation between mass and EW, we find a significant lack of massive galaxies with high EW, which could be explained if the most massive galaxies were more dusty and/or contained more neutral gas than less massive objects. Finally we find that more than half of the galaxies contain small but non negligible amounts of dust: the mean E(B-V) and the EW are well correlated, although with a large scatter, as already found at lower redshift
We thoroughly explore the properties of (sub)-millimeter (mm) selected galaxies (SMGs) in the Shark semi-analytic model of galaxy formation. Compared to observations, the predicted number counts at wavelengths (lambda) 0.6-2mm and redshift distributi
ons at 0.1-2mm, agree well. At the bright end (>1mJy), Shark galaxies are a mix of mergers and disk instabilities. These galaxies display a stacked FUV-to-FIR spectrum that agrees well with observations. We predict that current optical/NIR surveys are deep enough to detect bright (>1mJy) lambda=0.85-2mm-selected galaxies at z<5, but too shallow to detect counterparts at higher redshift. A James Webb Space Telescope 10,000s survey should detect all counterparts for galaxies with $S_{rm 0.85mm}>0.01$mJy. We predict SMGs disks contribute significantly (negligibly) to the rest-frame UV (IR). We investigate the 0<z<6 evolution of the intrinsic properties of >1mJy lambda=0.85-2mm-selected galaxies finding their: (i) stellar masses are $>10^{10.2}M_{odot}$, with the 2mm ones tracing the most massive galaxies ($>10^{11}M_{odot}$); (ii) specific star formation rates (SFR) are mildly (~3-10x) above the main sequence (MS); (iii) host halo masses are $gtrsim 10^{12.3}M_{odot}$, with 2mm galaxies tracing the most massive halos (proto-clusters); (iv) SMGs have lower dust masses ($approx 10^{8}M_{odot}$), higher dust temperatures ($approx 40-45$K) and higher rest-frame V-band attenuation (>1.5) than MS galaxies; (v) sizes decrease with redshift, from 4kpc at z=1 to <1kpc at z=4; (vi) the Carbon Monoxide line spectra of $S_{rm 0.85mm}>1$mJy sources peak at 4->3. Finally, we study the contribution of SMGs to the molecular gas and cosmic SFR density at 0<z<10, finding that >1mJy sources make a negligible contribution at z>3 and z>5, respectively, suggesting current observations have unveiled the majority of the star formation at 0<z<10.
We review the physical properties of nearby, relatively luminous galaxies, using results from newly available massive data sets together with more detailed observations. First, we present the global distribution of properties, including the optical a
nd ultraviolet luminosity, stellar mass, and atomic gas mass functions. Second, we describe the shift of the galaxy population from late galaxy types in underdense regions to early galaxy types in overdense regions. We emphasize that the scaling relations followed by each galaxy type change very little with environment, with the exception of some minor but detectable effects. The shift in the population is apparent even at the densities of small groups and therefore cannot be exclusively due to physical processes operating in rich clusters. Third, we divide galaxies into four crude types -- spiral, lenticular, elliptical, and merging systems -- and describe some of their more detailed properties. We attempt to put these detailed properties into the global context provided by large surveys.
We investigate the physical and morphological properties of LBGs at z ~2.5 to ~3.5, to determine if and how they depend on the nature and strength of the Lyalpha emission. We selected U-dropout galaxies from the z-detected GOODS MUSIC catalog, by ada
pting the classical Lyman Break criteria on the GOODS filter set. We kept only those galaxies with spectroscopic confirmation, mainly from VIMOS and FORS public observations. Using the full multi-wavelength 14-bands photometry, we determined the physical properties of the galaxies, through a standard spectral energy distribution fitting with the updated Charlot & Bruzual (2009) templates. We also added other relevant observations, i.e. the 24mu m observations from Spitzer/MIPS and the 2 MSec Chandra X-ray observations. Finally, using non parametric diagnostics (Gini, Concentration, Asymmetry, M_20 and ellipticity), we characterized the rest-frame UV morphology of the galaxies. We then analyzed how these physical and morphological properties correlate with the presence of the Lyalpha line in the optical spectra. We find that, unlike at higher redshift, the dependence of physical properties on the Lyalpha line is milder: galaxies without Lyalpha in emission tend to be more massive and dustier than the rest of the sample, but all other parameters, ages, SFRs, X-ray emission as well as UV morphology do not depend strongly on the presence of the line emission. A simple scenario where all LBGs have intrinsically high Lyalpha emission, but where dust and neutral hydrogen content (which shape the final appearance of the Lyalpha) depend on the mass of the galaxies, is able to reproduce the majority of the observed properties at z~3. Some modification might be needed to account for the observed evolution of these properties with cosmic epoch, which is also discussed.
We present a study of the Lyalpha forest at z<0.4 from which we conclude that at least 20% of the total baryons in the universe are located in the highly-ionized gas traced by broad Lyalpha absorbers. The cool photoionized low-z intergalactic medium
(IGM) probed by narrow Lyalpha absorbers contains about 30% of the baryons. We further find that the ratio of broad to narrow Lyalpha absorbers is higher at z<0.4 than at 1.5<z<3.6, implying that a larger fraction of the low redshift universe is hotter and/or more kinematically disturbed. We base these conclusions on an analysis of 7 QSOs observed with both FUSE and the HST/STIS E140M ultraviolet echelle spectrograph. Our sample has 341 HI absorbers with a total unblocked redshift path of 2.064. The observed absorber population is complete for log N_HI>13.2, with a column density distribution f(N_HI) propto N^-beta_HI. For narrow (b<40 km/s) absorbers beta = 1.76+/-0.06. The distribution of the Doppler parameter b at low redshift implies two populations: narrow (b<40 km/s) and broad (b>40 km/s) Lyalpha absorbers (referred to as NLAs and BLAs, respectively). Both the NLAs and some BLAs probe the cool (T~10^4 K) photoionized IGM. The BLAs also probe the highly-ionized gas of the warm-hot IGM (T~10^5-10^6 K). The distribution of b has a more prominent high velocity tail at z<0.4 than at 1.5<z<3.6, which results in median and mean b-values that are 15-30% higher at low z than at high z. The ratio of the number density of BLAs to NLAs at z<0.4 is a factor of ~3 higher than at 1.5<z<3.6.
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