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Register a new userTruncated Star Formation in Compact Groups of Galaxies: A Stellar Population Study
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Added by
Ignacio G. de la Rosa
Publication date
2006
fields
Physics
and research's language is
English
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We present the results of a study comparing the stellar populations in the elliptical galaxies of Hickson Compact Groups (HCGs) with those in low density environments. Three different population synthesis models and stellar population analyses are used to make the results more robust. The low-sigma galaxies in HCGs show an enhanced [Mg/Fe] ratio and a depleted metallicity [Z/H] with respect to their counterparts in the field. This behavior is interpreted as evidence for the action of a mechanism which truncated the star formation (SF). Hydrodynamical simulations of galaxy mergers (Di Matteo et al. 2005) support this interpretation by predicting the quenching of star formation soon after the merger event. Combining this scenario and the evidence presented here, the HCGs, generally considered to be ideal environments for galaxy-galaxy interactions, become ideal places for SF truncation.
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A series of population models are designed to explore the star formation history of gas-rich, low surface brightness (LSB) galaxies. LSB galaxies are unique in having properties of very blue colors, low H$alpha$ emission and high gas fractions that indicated a history of constant star formation (versus the declining star formation models used for most spirals and irregulars). The model simulations use an evolving multi-metallicity composite population that follows a chemical enrichment scheme based on Milky Way observations. Color and time sensitive stellar evolution components (i.e., BHB, TP-AGB and blue straggler stars) are included, and model colors are extended into the Spitzer wavelength regions for comparison to new observations. In general, LSB galaxies are well matched to the constant star formation scenario with the variation in color explained by a fourfold increase/decrease in star formation over the last 0.5 Gyrs (i.e., weak bursts). Early-type spirals, from the S$^4$G sample, are better fit by a declining star formation model where star formation has decreased by 40% in the last 12 Gyrs.
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I. Y. Izotova Astronomical Observatory ofn Taras Shevchenko National University of Kyiv
, Kyiv
2018
We use the data for the Hbeta emission-line, far-ultraviolet (FUV) and mid-infrared 22 micron continuum luminosities to estimate star formation rates <SFR> averaged over the galaxy lifetime for a sample of about 14000 bursting compact star-forming galaxies (CSFGs) selected from the Data Release 12 (DR12) of the Sloan Digital Sky Survey (SDSS). The average coefficient linking <SFR> and the star formation rate SFR_0 derived from the Hbeta luminosity at zero starburst age is found to be 0.04. We compare <SFR>s with some commonly used SFRs which are derived adopting a continuous star formation during a period of ~100 Myr, and find that the latter ones are 2-3 times higher. It is shown that the relations between SFRs derived using a geometric mean of two star-formation indicators in the UV and IR ranges and reduced to zero starburst age have considerably lower dispersion compared to those with single star-formation indicators. We suggest that our relations for <SFR> determination are more appropriate for CSFGs because they take into account a proper temporal evolution of their luminosities. On the other hand, we show that commonly used SFR relations can be applied for approximate estimation within a factor of ~2 of the <SFR> averaged over the lifetime of the bursting compact galaxy.
We present a multi-wavelength analysis of three compact galaxy groups, HCGs 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, HST, Spitzer) and ground-based (LCO, CTIO) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 associates (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (a) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (b) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.
In the last decade, extended stellar clusters with masses in the range from a few 10^4 to 10^8 M_sun have been found in various types of galaxies in different environments. Objects with masses comparable to normal globular clusters (GCs) are called extended clusters (ECs), while objects with masses in the dwarf galaxy regime are called ultra-compact dwarf galaxies (UCDs). In heavily interacting galaxies star clusters tend to form in larger conglomerations called star cluster complexes (CCs). In this work we systematically scan a suitable parameter space for CCs and perform numerical simulations to study their further fate. The varied sizes and masses of the CCs cover a matrix of 5x6 values with CC Plummer radii between 10 - 160 pc and CC masses between 10^5.5 - 10^8 M_sun, which are consistent with observed CC parameters. The CCs of the parametric study are on orbits with distances between 20 kpc and 60 kpc. In addition, we studied also the evolution of CCs on a circular orbit at a distance of 60 kpc to verify that also extremely extended ECs and UCDs can be explained by our formation scenario. All 54 simulations end up with stable merger objects, wherein 26 to 97% of the initial CC mass is bound. The objects show a general trend of increasing effective radii with increasing mass. Despite the large range of input Plummer radii of the CCs (10 to 160 pc) the effective radii of the merger objects are constrained to values between 10 and 20 pc at the low mass end and to values between 15 and 55 pc at the high mass end. The structural parameters of the models are comparable to those of the observed ECs and UCDs. The results of the circular orbits demonstrate that even very extended objects like the M31 ECs found by Huxor in 2005 and the very extended (r_eff > 80 pc), high-mass UCDs can be explained by merged cluster complexes in regions with low gravitational fields at large distances.
A 1-truncated compact Lie group is any extension of a finite group by a torus. In this note we compute the homotopy types of $Map_*(BG,BH)$, $Map(BG,BH)$, and $Map(EG, B_GH)^G$ for compact Lie groups $G$ and $H$ with $H$ 1-truncated, showing that they are computed entirely in terms of spaces of homomorphisms from $G$ to $H$. These results generalize the well-known case when $H$ is finite, and the case of $H$ compact abelian due to Lashof, May, and Segal.
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