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- All Subjects: Red shift
- Creators: Malhotra, Sangeeta
Description
The first part of this dissertation presents the implementation of Bayesian statistics with galaxy surface luminosity (SL) prior probabilities to improve the ac- curacy of photometric redshifts. The addition of the SL prior probability helps break the degeneracy of spectro-photometric redshifts (SPZs) between low redshift 4000 A break galaxies and high redshift Lyman break galaxies which are mostly catas- trophic outliers. For a sample of 1138 galaxies with spectroscopic redshifts in the GOODS North and South fields at z < 1.6, the application of the surface luminosity prior reduces the fraction of galaxies with redshift deviation sigma(z) > 0.2 from 15.0% to 10.4%. The second part of this dissertation presents the study of the chemical evolution of the star-forming galaxies. The Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) grism Survey effectively selects emission line galaxies (ELGs) to mAB ~ 27. Follow-up Magellan LDSS3+IMACS spectroscopy of the HST/ACS PEARS ELGs confirms an accuracy of sigma_z = 0.006 for the HST/ACS PEARS grism redshifts. The luminosity-metallicity (L-Z) relation and the mass-metallicity (M-Z) relation of the PEARS ELGs at z ~ 0.6 are offset by ~ - 0.8 dex in metallicity for a given rest-frame B absolute magnitude and stellar mass relative to the local relations from SDSS galaxies. The offsets in both relations are ~ - 0.4 dex larger than that given by other samples at same redshifts, which are demonstrated to be due to the selection of different physical properties of the PEARS ELGs: low metallicities, very blue colors, small sizes, compact disturbed morphologies, high SSFR > 10^-9 yr^-1 , and high gas fraction. The downsizing effect, the tidal interacting induced inflow of metal-poor gas, and the SNe driven galactic winds outflows, may account for the significant offset of the PEARS galaxies in the L-Z and the M-Z relations relative to the local relations. The detection of the emission lines of ELGs down to m ~ 26 mag in the HST/ACS PEARS + HST/WCF3 ERS NIR composit grism spectra enables to extend the study of the evolution of the L-Z and M-Z relations to 0.6 < z < 2.4.
ContributorsXia, Lifang (Author) / Malhotra, Sangeeta (Thesis advisor) / Rhoads, James (Committee member) / Scannapieco, Evan (Committee member) / Jansen, Rolf (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2012
Description
Green pea galaxies are a class of rare, compact starburst galaxies that have powerful optical emission line [OIII]$\lambda$5007. They are the best low-redshift analogs of high-redshift (z$>$2) Lyman-alpha emitting galaxies (LAEs). They provide unique opportunities to study physical conditions in high-redshift LAEs in great detail. In this dissertation, a few physical properties of green peas are investigated. The first study in the dissertation presents star formation rate (SFR) surface density, thermal pressure in HII regions, and a correlation between them for 17 green peas and 19 Lyman break analogs, which are nearby analogs of high-redshift Lyman break galaxies. This correlation is consistent with that found from the star-forming galaxies at z $\sim$ 2.5. In the second study, a new large sample of 835 green peas in the redshift range z = 0.011 -- 0.411 are assembled from Data Release 13 of the Sloan Digital Sky Survey (SDSS) with the equivalent width of the line [OIII]$\lambda$5007 $>$ 300\AA\ or the equivalent width of the line H$\beta$ $>$ 100\AA. The size of this new sample is ten times that of the original 80 star-forming green pea sample. With reliable T$_e$-based gas-phase metallicity measurements for the 835 green peas, a new empirical calibration of R23 (defined as ([OIII]$\lambda$$\lambda$4959,5007 + [OII]$\lambda$$\lambda$3726,3729)/H$\beta$) for strong line emitters is then derived. The double-value degeneracy of the metallicity is broken for galaxies with large ionization parameter (which manifests as log([OIII]$\lambda$$\lambda$4959,5007/[OII]$\lambda$$\lambda$3726,3729) $\geq$ 0.6). This calibration offers a good way to estimate metallicities for extreme emission-line galaxies and high-redshift LAEs. The third study presents stellar mass measurements and the stellar mass-metallicity relation of 828 green peas from the second study. The stellar mass covers 6 orders of magnitude in the range 10$^{5}$ -- 10$^{11}$ M$_{\odot}$, with a median value of 10$^{8.8}$ M$_{\odot}$. The stellar mass-metallicity relation of green peas is flatter and displays about 0.2 - 0.5 dex offset to lower metallicities in the range of stellar mass higher than 10$^{8}$ M$_{\odot}$ compared to the local SDSS star-forming galaxies. A significant dependence of the stellar mass-metallicity relation on star formation rate is not found in this work.
ContributorsJiang, Tianxing (Author) / Malhotra, Sangeeta (Thesis advisor) / Rhoads, James E (Committee member) / Scannapieco, Evan (Committee member) / Borthakur, Sanchayeeta (Committee member) / Jansen, Rolf A (Committee member) / Arizona State University (Publisher)
Created2018
Description
New measurements of the Hα luminosity function (LF) and star formation rate
(SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field.
These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique
infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and
sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ).
The present sample, based on a single DAWN field, contains 116 Hα emission-
line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These
candidates have been selected through comparison of narrow and broad-band images
in the infrared and through matching with existing catalogs in the COSMOS field.
The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92
erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From
this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An
additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint
end slope and luminosity density that are derived are consistent with prior results at
similar redshifts, with reduced uncertainties.
An analysis of these Hα emitters’ sizes is also presented, showing a direct corre-
lation between the galaxies’ sizes and their Hα emission.
(SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field.
These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique
infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and
sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ).
The present sample, based on a single DAWN field, contains 116 Hα emission-
line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These
candidates have been selected through comparison of narrow and broad-band images
in the infrared and through matching with existing catalogs in the COSMOS field.
The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92
erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From
this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An
additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint
end slope and luminosity density that are derived are consistent with prior results at
similar redshifts, with reduced uncertainties.
An analysis of these Hα emitters’ sizes is also presented, showing a direct corre-
lation between the galaxies’ sizes and their Hα emission.
ContributorsGonzalez, Alicia (Author) / Rhoads, James E (Thesis advisor) / Malhotra, Sangeeta (Thesis advisor) / Butler, Nathaniel (Committee member) / Jansen, Rolf (Committee member) / Arizona State University (Publisher)
Created2017