The Star Formation History of the Virgo Early‐Type Galaxy NGC 4435: TheSpitzerMid‐Infrared View

AbstractWe combine deep UBV RIzJK photometry from the MUSYC survey with redshifts from the COMBO-17 survey to study the rest-frame ultraviolet (UV) properties of 674 high-redshift (0.5 < z < 1) early-type galaxies, drawn from the Extended Chandra Deep Field South (E-CDFS). Galaxy morphologies are determined through visual inspection of Hubble Space Telescope (HST) images taken from the GEMS survey. We harness the sensitivity of the UV to young (<1 Gyrs old) stars to quantify the recent star formation history of the early-type population. We find compelling evidence that early-types of all luminosities form stars over the lifetime of the Universe, although the bulk of their star formation is already complete at high redshift. Luminous (−23 < M(V) < −20.5) early-types form 10-15 percent of their mass after z = 1, while their less luminous (M(V) > −20.5) counterparts form 30-60 percent of their mass in the same redshift range.

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Star Formation History of Early-Type Galaxies with Tidal Debris in the S4G

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314004906 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 129-129

Author(s):

Beatriz H. F. Ramos ◽

Karín Menéndez-Delmestre ◽

Taehyun Kim ◽

Kartik Sheth ◽

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Stellar Structure ◽

Star Formation History ◽

Early Type ◽

Uv Emission ◽

Optical Images ◽

Formation History ◽

History Of ◽

Stellar Masses

AbstractLocal early-type galaxies (ETGs), despite typically being associated to old stellar populations and passive evolution, have been in some cases observed to present peculiarities in their stellar structure, like disks and shells (e.g., Kormendy et al.1997, Rix, Carollo & Freeman 1999). Moreover, it has been observed that ETGs with such tidal features may present UV emission (Rampazzo et al.2007, Salim & Rich 2010). These properties make them relevant constraints to galaxy formation models. We are analysing the structure of nearby ETGs observed in the Spitzer Survey of Stellar Structure in Galaxies (S4G; Sheth et al.2010), which comprises the largest mid-IR survey of galaxies in the local Universe. We perform a 2D GALFIT decomposition of the 3.6μm images of 146 ETGs and examine their residual images. We identify tidal features in 17% of these, suggesting that a non-negligible ETGs fraction may have experienced (after the formation of the bulk of their stellar budget) merger events that have left signatures (Canalizo et al.2007). For 6 of these peculiar ETGs, we also applied GALFIT decomposition to public GALEX/UV and SDSS/optical images. With measurements in multiple bands, we applied SED fitting techniques to estimate star formation rates (SFR) and stellar masses for the galaxies and their tidal features. We find that these 6 peculiar ETGs present masses in agreement with the population of non-peculiar ETGs. However, SFRs are higher than what has been measured for the average ETG population (Shapiro et al.2010, SDSS MPA-JHU catalog). Based on the Kaviraj (2010) relation, we find that for these peculiar ETGs the estimated age of the most recent star formation event is less than 3Gyrs. Despite this indication of recent star formation, we have not found evidence of prominent UV emission in the tidal features (Marino et al.2010). We are currently extending our work to the full sample of peculiar ETGs identified in our sample.

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The star-formation histories of early-type galaxies from ATLAS3D

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312009167 ◽

2011 ◽

Vol 7 (S284) ◽

pp. 244-247 ◽

Cited By ~ 1

Author(s):

Richard M. McDermid ◽

Katherine Alatalo ◽

Leo Blitz ◽

Maxime Bois ◽

Frédéric Bournaud ◽

...

Keyword(s):

Star Formation ◽

Stellar Population ◽

Abundance Ratio ◽

Star Formation History ◽

Early Type ◽

Solar Abundance ◽

Formation History ◽

History Of ◽

Free Parameters ◽

Star Formation Histories

AbstractWe present an exploration of the integrated stellar populations of early-type galaxies (ETGs) from the ATLAS3D survey. We use two approaches: firstly the application of line-indices interpreted through single stellar population (SSP) models, which provide a single value of age, metallicity and abundance ratio. And secondly, by fitting a linear combination of SSP spectra to our data, smoothly weighted in the free parameters of age and metallicity, thereby inferring a star-formation history of these galaxies. Despite the significant differences in these approaches, we obtain generally consistent results, such that galaxies that are more massive appear older with enhanced abundance ratios using line indices, and have shorter star-formation histories weighted to early times. We highlight two limitations of the index-SSP approach. Firstly the SSP-equivalent ages belie the fact that ETGs are overwhelmingly composed of ancient stars. Secondly, the young stellar contributions implied in our star formation histories are required to obtain realistic UV-optical colours. We remark that, even fitting solar-abundance models, we can recover a star-formation duration that correlates with the measured alpha-enhancement, in agreement with other recent work.

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Stellar Populations in Mixed Pairs of Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900109477 ◽

1995 ◽

Vol 164 ◽

pp. 434-434 ◽

Cited By ~ 1

Author(s):

D.F. De Mello ◽

W.C. Keel ◽

J.W. Sulentic ◽

R. Rampazzo

Keyword(s):

Star Formation ◽

Stellar Population ◽

Elliptical Galaxy ◽

Star Formation History ◽

Population Synthesis ◽

Early Type ◽

Stellar Content ◽

Stellar Population Synthesis ◽

History Of ◽

Early Type Galaxy

The interpration of the interaction in galaxies is simplified in mixed pairs (E+S) because most or all of the cold gas can be traced to an origin in a single galaxy (S). We used spectroscopy, imaging, far–IR, and stellar population synthesis to study the stellar content and history of star formation in the nuclear region of the early–type galaxy in the mixed pair AM0327–285. We used the procedure for stellar population synthesis developed by Bica (1988) to estimate the star-formation history of the nucleus of the elliptical galaxy. The method uses a library of star clusters, and estimates the chemical evolution in a test population with two parameters: age and metallicity; no assumptions on gravity or details of stellar evolution are necessary, and the IMF is implicit in the cluster spectra. The procedure allows one to both determine the chemical enrichment and date successive generations of star formation. The result indicates that the dominant population is old and metal–rich ([Z/Z]⊙=0.3), while ~ 10% of the flux at 5870 Å arises from a young stellar population (age ≤ 5 × 108 yr), confirming that this early-type galaxy had recent star formation as suggested also by photometry and far–IR data (de Mello et al 1994). This age is close to several estimates of the characteristic timescale of the interaction, suggesting that the mass influx associated with this star formation occurred as a result of an earlier phase of the interaction and not as a result of the present geometry of the pair.

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