Evolution of the Ultraviolet Upturn at 0.3 < z < 1: Exploring Helium-rich Stellar Populations

Abstract We measure the near-UV (rest-frame ∼2400 Å) to optical color for early-type galaxies in 12 clusters at 0.3 < z < 1.0. We show that this is a suitable proxy for the more common far-ultraviolet bandpass used to measure the ultraviolet upturn and find that the upturn is detected to z = 0.6 in these data, in agreement with previous work. We find evidence that the strength of the upturn starts to wane beyond this redshift and largely disappears at z = 1. Our data are most consistent with models where early-type galaxies contain minority stellar populations with non-cosmological helium abundances, up to around 46%, formed at z ≥ 3, resembling globular clusters with multiple stellar populations in our Galaxy. This suggests that elliptical galaxies and globular clusters share similar chemical evolution and star formation histories. The vast majority of the stellar mass in these galaxies also must have been in place at z > 3.

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Star formation histories of resolved galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031718 ◽

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.

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

Modern Physics Letters A ◽

10.1142/s021773230802608x ◽

2008 ◽

Vol 23 (03) ◽

pp. 153-167 ◽

Cited By ~ 14

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.

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Connections between MWG Star Clusters and Dwarf Galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314005742 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 275-277

Author(s):

Kim A. Venn

Keyword(s):

Star Formation ◽

Globular Clusters ◽

Dwarf Galaxies ◽

Star Clusters ◽

Theoretical Models ◽

Stellar Populations ◽

Observational Evidence ◽

Paradigm Shifts ◽

The Past ◽

Star Formation Histories

It seems that in the past decade, there have been two paradigm shifts regarding star clusters. Firstly, the observational evidence for multiple stellar populations requires more extended and often complex star formation histories in star clusters. Secondly, theoretical models that form globular clusters in dwarf galaxies that are accreted at very early epochs (z > 5) are able to reproduce the age-metallicity relations observed. For the accretion scenario to be viable, globular clusters should also resemble the chemistry of at least some dwarf galaxies.

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The stellar populations of massive galaxies in the local Universe

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313005085 ◽

2012 ◽

Vol 8 (S295) ◽

pp. 290-299

Author(s):

Richard M. McDermid

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Stellar Population ◽

Stellar Populations ◽

Early Type ◽

Massive Galaxies ◽

Spatially Resolved ◽

Low Mass ◽

Galaxy Environment ◽

Star Formation Histories

AbstractI present a brief review of the stellar population properties of massive galaxies, focusing on early-type galaxies in particular, with emphasis on recent results from the ATLAS3D Survey. I discuss the occurence of young stellar ages, cold gas, and ongoing star formation in early-type galaxies, the presence of which gives important clues to the evolutionary path of these galaxies. Consideration of empirical star formation histories gives a meaningful picture of galaxy stellar population properties, and allows accurate comparison of mass estimates from populations and dynamics. This has recently provided strong evidence of a non-universal IMF, as supported by other recent evidences. Spatially-resolved studies of stellar populations are also crucial to connect distinct components within galaxies to spatial structures seen in other wavelengths or parameters. Stellar populations in the faint outer envelopes of early-type galaxies are a formidable frontier for observers, but promise to put constraints on the ratio of accreted stellar mass versus that formed ‘in situ’ - a key feature of recent galaxy formation models. Galaxy environment appears to play a key role in controlling the stellar population properties of low mass galaxies. Simulations remind us, however, that current day galaxies are the product of a complex assembly and environment history, which gives rise to the trends we see. This has strong implications for our interpretation of environmental trends.

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The Spatially-Resolved Star Formation History of the M31 Disk from Resolved Stellar Populations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314009302 ◽

2014 ◽

Vol 10 (S309) ◽

pp. 57-60

Author(s):

Alexia R. Lewis ◽

Julianne J. Dalcanton ◽

Andrew E. Dolphin ◽

Daniel R. Weisz ◽

Benjamin F. Williams ◽

...

Keyword(s):

Star Formation ◽

Stellar Populations ◽

Star Formation History ◽

Star Forming ◽

Spatially Resolved ◽

Star Forming Regions ◽

Star Formation Activity ◽

Individual Star ◽

Star Formation Histories ◽

Optical Color

AbstractThe Panchromatic Hubble Andromeda Treasury (PHAT) is an HST multi-cycle treasury program that has mapped the resolved stellar populations of ∼1/3 of the disk of M31 from the UV through the near-IR. This data provides color and luminosity information for more than 150 million stars. Using stellar evolution models, we model the optical color-magnitude diagram to derive spatially-resolved recent star formation histories (SFHs) over large areas of M31 with 100 pc resolution. These include individual star-forming regions as well as quiescent portions of the disk. With these gridded SFHs, we create movies of star formation activity to study the evolution of individual star-forming events across the disk. We analyze the structure of star formation and examine the relation between star formation and gas throughout the disk and particularly in the 10-kpc star-forming ring. We find that the ring has been continuously forming stars for at least 500 Myr. As the only large disk galaxy that is close enough to obtain the photometry for this type of spatially-resolved SFH mapping, M31 plays an important role in our understanding of the evolution of an L* galaxy.

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Early-type galaxy formation history from GALEX-SAURON

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308017638 ◽

2007 ◽

Vol 3 (S245) ◽

pp. 193-194

Author(s):

Hyunjin Jeong ◽

Sukyoung K. Yi ◽

Martin Bureau ◽

Davor Kranović ◽

Roger L. Davies

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Classical Model ◽

Stellar Populations ◽

Elliptical Galaxies ◽

Early Type ◽

Secondary Star ◽

Rich Diversity ◽

Formation History

One of long-standing debates in modern astrophysics is the formation mechanism of early-type galaxies. The classical model, proposed by Eggel et al. (1962), explains that early-type stellar populations form in an initial highly efficient burst and evolve without further star formation until present day. The high Mg and alpha abundances found in bright elliptical galaxies support such scenarios. Early-type galaxies, therefore, are traditionally believed that they are dynamically simple stellar systems with homogeneous stellar populations (e.g. Gott 1977). The popular Lambda Cold Dark Matter (LCDM) paradigm (e.g. Toomre and Toomre 1972), however, strongly suggested a hierarchical merger picture for massive elliptical galaxies. In this model, early-type galaxies form as a result of major mergers and are thought to have continued star formation. Evidence is growing that a substantial fraction of early-type galaxies has secondary star formation. Furthermore, SAURON survey has revealed a rich diversity in the kinematics, discovering numerous central disks and kinematically decoupled cores (e.g. Emsellem et al. 2004; Sarzi et al. 2006). Early-type galaxies are thus likely to have had complex and varied formation histories.

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Unveiling the afterlife of galaxies with ultraviolet data

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320001611 ◽

2020 ◽

Vol 15 (S359) ◽

pp. 467-468

Author(s):

Ariel Werle

Keyword(s):

Star Formation ◽

Gini Index ◽

Stellar Populations ◽

Optical Spectra ◽

Early Type ◽

Combined Analysis ◽

Early Results ◽

Star Formation Histories ◽

Red Sequence

Abstract. Recent works have shown that early-type galaxies (ETGs) are much more complex than early studies suggested. We present early results from a combined analysis of optical spectra and ultraviolet photometry for a sample of 3453 red sequence galaxies in at z < 0.1 that are classified as elliptical by Galaxy Zoo. By measuring the Gini index of the star-formation histories derived by starlight, we investigate the complexity of the mixture of stellar populations required to describe ETGs in our sample. When fitting only optical spectra, starlight assigns more or less the same mixture of stellar populations to all ETGs, while the addition of UV data unveils a bimodallity in the star-formation histories of these galaxies. We find evidence for stellar populations younger than 1 Gyr in 17 per cent of our sample, indicating that some galaxies do not stay permanently quenched after reaching the red sequence.

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