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dc.creatorFisher, David B.en_US
dc.creatorDrory, Niven_US
dc.creatorFabricius, Maximillian H.en_US
dc.date.accessioned2016-04-28T19:43:27Z
dc.date.available2016-04-28T19:43:27Z
dc.date.issued2009-05en
dc.identifierdoi:10.15781/T2GV5X
dc.identifier.citationFisher, David B., Niv Drory, and Maximilian H. Fabricius. "Bulges of nearby galaxies with Spitzer: The growth of pseudobulges in disk galaxies and its connection to outer disks." The Astrophysical Journal, Vol. 697, No. 1 (May., 2009): 630.en_US
dc.identifier.issn0004-637Xen_US
dc.identifier.urihttp://hdl.handle.net/2152/35171
dc.description.abstractWe study star formation rates (SFRs) and stellar masses in bulges of nearby disk galaxies. For this we construct a new SFR indicator that linearly combines data from the Spitzer Space Telescope and the Galaxy Evolution Explorer. All bulges are found to be forming stars irrespective of bulge type (pseudobulge or classical bulge). At present-day SFR the median pseudobulge could have grown the present-day stellar mass in 8 Gyr. Classical bulges have the lowest specific SFR implying a growth times that are longer than a Hubble time, and thus the present-day SFR does not likely play a major role in the evolution of classical bulges. In almost all galaxies in our sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk. This suggests that almost all galaxies are increasing their B/T through internal star formation. The SFR in pseudobulges correlates with their structure. More massive pseudobulges have higher SFR density, this is consistent with that stellar mass being formed by moderate, extended star formation. Bulges in late-type galaxies have similar SFRs as pseudobulges in intermediate-type galaxies, and are similar in radial size. However, they are deficient in mass; thus, they have much shorter growth times, similar to 2 Gyr. We identify a class of bulges that have nuclear morphology similar to pseudobulges, significantly lower specific SFR than pseudobulges, and are closer to classical bulges in structural parameter correlations. These are possibly composite objects, evolved pseudobulges or classical bulges experiencing transient, enhanced nuclear star formation. Our results are consistent with a scenario in which bulge growth via internal star formation is a natural, and near ubiquitous phenomenon in disk galaxies. Those galaxies with large classical bulges are not affected by the in situ bulge growth, likely because the majority of their stellar mass comes from some other phenomenon. Yet, those galaxies without a classical bulge, over long periods of extended star formation are able to growth a pseudobulge. Though cold accretion is not ruled out, for pseudobulge galaxies an addition of stellar mass from mergers or accretion is not required to explain the bulge mass. In this sense, galaxies with pseudobulges may very well be bulgeless (or "quasi-bulgeless") galaxies, and galaxies with classical bulges are galaxies in which both internal evolution and hierarchical merging are responsible for the bulge mass by fractions that vary from galaxy to galaxy.en_US
dc.description.sponsorshipNSF AST 06-07490en_US
dc.description.sponsorshipNASA NAS 5-26555en_US
dc.language.isoEnglishen_US
dc.relation.ispartofen_US
dc.rightsAdministrative deposit of works to Texas ScholarWorks: This works author(s) is or was a University faculty member, student or staff member; this article is already available through open access or the publisher allows a PDF version of the article to be freely posted online. The library makes the deposit as a matter of fair use (for scholarly, educational, and research purposes), and to preserve the work and further secure public access to the works of the University.en_US
dc.subjectgalaxies: bulgesen_US
dc.subjectgalaxies: evolutionen_US
dc.subjectgalaxies: formationen_US
dc.subjectgalaxies:en_US
dc.subjectfundamental parametersen_US
dc.subjectgalaxies: structureen_US
dc.subjectcentral mass concentrationsen_US
dc.subjecthubble-space-telescopeen_US
dc.subjectdark-matter halosen_US
dc.subjectlate-type spiralsen_US
dc.subjectstar-formationen_US
dc.subjectsecular evolutionen_US
dc.subjectbarred galaxiesen_US
dc.subjectgalactic disksen_US
dc.subjectstellar populationsen_US
dc.subjectclassical bulgesen_US
dc.subjectastronomy & astrophysicsen_US
dc.titleBulges Of Nearby Galaxies With Spitzer: The Growth Of Pseudobulges In Disk Galaxies And Its Connection To Outer Disksen_US
dc.typeReviewen_US
dc.description.departmentAstronomyen_US
dc.identifier.Filename2009_05_spitzer.pdfen_US
dc.rights.restrictionOpenen_US
dc.identifier.doi10.1088/0004-637x/697/1/630en_US
dc.contributor.utaustinauthorFisher, David B.en_US
dc.relation.ispartofserialAstrophysical Journalen_US


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