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Spatially Resolved Galaxy Star Formation and its Environmental Dependence

Welikala, Niraj (2009) Spatially Resolved Galaxy Star Formation and its Environmental Dependence. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The role of star formation in galaxiesis clearly a fundamental component of their evolution, although itis becoming clear that galaxy environments may also play a significantrole. To explore the relationship between environment and star formationin galaxies, I use the photometric information contained in individualpixels of 44,964 galaxies (volume-limited) fromthe Fourth Data Release of the Sloan Digital Sky Survey. Iuse the pixel-z technique, which combines stellar population synthesis modelswith photometric redshift template fitting on the scale of individualpixels in galaxy images. Spectral energy distributions are constructed, sampling a wide range ofproperties such as age, star formation rate (SFR), dust obscuration andmetallicity. By summing the SFRs in the pixels, I show that, as found in other studies, thedistribution of total galaxy SFR shifts to lower values as the local densityof surrounding galaxies increases. The effectis most prominent in the galaxies with the highest SFR. Since the method enables an estimate to be made of the spatial distribution of star formation within galaxies, the mean SFR of each galaxy is then calculated asa function of radius. I find that, on average, the mean SFR is dominatedby star formation in the central regions of galaxies and it is this centralstar formation that is suppressed in high density environments. The mean SFR in the outskirts of galaxies is found to be largely independentof environmental effects. These trends are shared by galaxieswhich are highly star forming.I also investigate the impact of the density-morphology relation of galaxies on the observed trends. Early-type and late-type galaxies exhibit distinct radial SFR distributions.A suppression of star formation in the highest density environments is still found in the highest star forming galaxies within each type. I show that the density-morphology relation alone cannot accountfor this observed suppression. This points to a mechanism by which the environment governs the evolution of galaxies, affecting the star formation in the innermost regions in both early and late-type galaxies. I suggest that this is a natural consequence of "downsizing" in galaxies.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairConnolly,
Committee CoChairKosowsky, Arthurkosowsky@pitt.eduKOSOWSKY
Committee MemberTurnshek, Daviddavidt@pitt.eduDAVIDT
Committee MemberCroft,
Committee MemberSavinov, Vladimirvps3@pitt.eduVPS3
Date: 29 January 2009
Date Type: Completion
Defense Date: 25 September 2008
Approval Date: 29 January 2009
Submission Date: 1 December 2008
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: galaxies: distances and redshifts; galaxies: evolution; galaxies: formation; galaxies: statistics; galaxies: structure
Other ID:, etd-12012008-155425
Date Deposited: 10 Nov 2011 20:07
Last Modified: 15 Nov 2016 13:52


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