scholarly journals Composite star formation histories of early-type galaxies from minor mergers: prospects for WFC3

2010 ◽  
pp. no-no ◽  
Author(s):  
S. Peirani ◽  
R. M. Crockett ◽  
S. Geen ◽  
S. Khochfar ◽  
S. Kaviraj ◽  
...  
Keyword(s):  
Star Formation ◽  
Early Type ◽  
Minor Mergers ◽  
Star Formation Histories

scholarly journals THE STAR FORMATION HISTORIES OF EARLY-TYPE GALAXIES: INSIGHTS FROM THE REST-FRAME ULTRAVIOLET

2008 ◽  
Vol 23 (03) ◽  
pp. 153-167 ◽  
Author(s):  
SUGATA KAVIRAJ
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
High Redshift ◽  
Stellar Mass ◽  
Early Type ◽  
Redshift Range ◽  
Colour Distribution ◽  
Type Population ◽  
Minor Mergers ◽  
Star Formation Histories

Our current understanding of the star formation histories of early-type galaxies is reviewed, in the context of recent observational studies of their ultraviolet (UV) properties. Combination of UV and optical spectro-photometric data indicates that the bulk of the stellar mass in the early-type population forms at high redshift (z>2), possibly over short timescales (<1 Gyr). Nevertheless, early-types of all luminosities form stars over the lifetime of the Universe, with most luminous (-23<M(V)<-21) systems forming 10–15% of their stellar mass after z = 1 (with a scatter to higher value), while their less luminous (M(V)>-21) counterparts form 30–60% of their mass in the same redshift range. The large scatter in the (rest-frame) UV colours in the redshift range 0<z<0.7 indicates widespread low-level star formation in the early-type population over the last 8 billion years. The mass fraction of young (<1 Gyr old) stars in luminous early-type galaxies varies between 1% and 6% at z ~ 0 and is in the range 5–13% at z ~ 0.7. The intensity of recent star formation and the bulk of the UV colour distribution is consistent with what might be expected from minor mergers (mass ratios ≲ 1:6) in a ΛCDM cosmology.

scholarly journals Star formation histories of resolved galaxies

2008 ◽  
Vol 4 (S258) ◽  
pp. 61-72
Author(s):  
Monica Tosi
Keyword(s):  
Star Formation ◽  
Observational Data ◽  
Stellar Populations ◽  
Morphological Type ◽  
The Other ◽  
Early Type ◽  
Significant Rate ◽  
Star Formation Histories

AbstractThe colour-magnitude diagrams of resolved stellar populations are the best tool to study the star formation histories of the host galactic regions. In this review the method to derive star formation histories by means of synthetic colour-magnitude diagrams is briefly outlined, and the results of its application to resolved galaxies of various morphological types are summarized. It is shown that all the galaxies studied so far were already forming stars at the lookback time reached by the observational data, independently of morphological type and metallicity. Early-type galaxies have formed stars predominantly, but in several cases not exclusively, at the earliest epochs. All the other galaxies appear to have experienced rather continuous star formation activities throughout their lifetimes, although with significant rate variations and, sometimes, short quiescent phases.

scholarly journals What drives the star formation in early-type galaxies at late epochs? - the case for minor mergers

2009 ◽  
Vol 5 (S262) ◽  
pp. 168-171 ◽  
Author(s):  
Sugata Kaviraj ◽  
Richard Ellis ◽  
Sukyoung Yi ◽  
Joseph Silk ◽  
Kevin Schawinski ◽  
...  
Keyword(s):  
Star Formation ◽  
Early Type ◽  
Principal Mechanism ◽  
Redshift Range ◽  
Low Level ◽  
Star Formation Activity ◽  
Multi Wavelength ◽  
Major Merger ◽  
Minor Mergers ◽  
Intermediate Redshift

AbstractMulti-wavelength photometry of early-type galaxies (ETGs) in the COSMOS survey is used to demonstrate that the low-level star formation activity in the ETG population at late epochs (z < 1) is likely to be driven by repeated minor mergers. While relaxed ETGs are almost entirely contained within the UV red sequence, their morphologically disturbed counterparts are largely found in the blue cloud, regardless of luminosity. Since empirically determined major-merger rates in the redshift range z < 1 are a few factors too low to account for the number fraction of disturbed ETGs, this suggests that minor mergers are the principal mechanism that drives star formation activity in ETGs at low and intermediate redshift.

scholarly journals A TALE OF A RICH CLUSTER ATz∼ 0.8 AS SEEN BY THE STAR FORMATION HISTORIES OF ITS EARLY-TYPE GALAXIES

2014 ◽  
Vol 797 (2) ◽  
pp. 136 ◽  
Author(s):  
Anna Ferré-Mateu ◽  
Patricia Sánchez-Blázquez ◽  
Alexandre Vazdekis ◽  
Ignacio G. de la Rosa
Keyword(s):  
Star Formation ◽  
Early Type ◽  
Rich Cluster ◽  
Star Formation Histories

scholarly journals Minor mergers: fundamental but unexplored drivers of galaxy evolution

2015 ◽  
Vol 11 (S319) ◽  
pp. 130-136
Author(s):  
Sugata Kaviraj
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Morphological Type ◽  
Disk Galaxies ◽  
Early Type ◽  
Gas Reservoirs ◽  
Star Formation Activity ◽  
Merger Process ◽  
Minor Mergers ◽  
Local Disk

AbstractWe use the SDSS Stripe 82 to study the stellar-mass growth that is triggered by minor mergers in local disk galaxies. Since major mergers destroy disks and create spheroids, morphologically disturbed spirals are likely remnants of minor mergers (since the disk remains intact). Disturbed spirals exhibit enhanced specific star formation rates (SSFRs), with the enhancement increasing in galaxies with ‘later’ morphological type (that have larger gas reservoirs and smaller bulges). By combining the SSFR enhancements with the fraction of time spirals in various morphological classes spend in this ‘enhanced’ mode, we estimate that ~40% of the star formation activity in local spirals is directly triggered by minor mergers. Combining our results with the star formation in local early-type galaxies – which is almost completely driven by minor mergers – suggests that around half the star formation activity at the present day is likely to be triggered by the minor-merger process.

scholarly journals Observational Comparison of Star Formation in Different Galaxy Types

2010 ◽  
Vol 6 (S270) ◽  
pp. 335-346
Author(s):  
Eva K. Grebel
Keyword(s):  
Star Formation ◽  
Variable Star ◽  
High Mass ◽  
Early Type ◽  
Intermediate Mass ◽  
Wide Range ◽  
Low Mass ◽  
Key Features ◽  
Star Formation Histories ◽  
Hubble Time

AbstractGalaxies cover a wide range of masses and star formation histories. In this review, I summarize some of the evolutionary key features of common galaxy types. At the high-mass end, very rapid, efficient early star formation is observed, accompanied by strong enrichment and later quiescence, well-described by downsizing scenarios. In the intermediate-mass regime, early-type galaxies may still show activity in low-mass environments or when being rejuvenated by wet mergers. In late-type galaxies, we find continuous, though variable star formation over a Hubble time. In the dwarf regime, a wide range of properties from bursty activity to quiescence is observed. Generally, stochasticity dominates here, and star formation rates and efficiencies tend to be low. Morphological types and their star formation properties correlate with environment.

scholarly journals Star Formation Histories of Dwarf Galaxies from the Colour-Magnitude Diagrams of Their Resolved Stellar Populations

2010 ◽  
Vol 2010 ◽  
pp. 1-25 ◽  
Author(s):  
Michele Cignoni ◽  
Monica Tosi
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Early Type ◽  
Significant Difference ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Show Evidence ◽  
History Of ◽  
Star Formation Histories

In this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize: (1) only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, orgasping, SF regimes; (2) a few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; (3) no galaxy experiencing now its first SF episode has been found yet; (4) no frequent evidence of strong SF bursts is found; (5) there is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed.

scholarly journals Understanding the growth of massive galaxies via stellar populations

2012 ◽  
Vol 8 (S295) ◽  
pp. 125-128
Author(s):  
Ignacio Ferreras
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Past History ◽  
Stellar Populations ◽  
Open Problems ◽  
Massive Galaxies ◽  
Spectroscopic Observations ◽  
Formation And Evolution ◽  
Minor Mergers ◽  
Star Formation Histories

AbstractThe formation and evolution of massive galaxies represent one of the most intriguing open problems in astrophysics. Their underlying stellar populations encode valuable information about their past history. Detailed spectroscopic observations allow us to constrain the star formation histories, revealing a complicated mixture of a strong, early formation process, followed by passive evolution in the cores, along with an extended assembly of the outer regions via minor mergers. In this contributed talk, some recent results are presented from the analysis of samples of massive galaxies both at z ~ 0 and moderate redshift.

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