An Inventory of the Stellar Initial Mass Function in Early-Type Galaxies

Tortora, C.; Romanowsky, Aaron J.; Napolitano, N. R.

doi:10.1088/0004-637x/765/1/8

Cited by 105 publications

(187 citation statements)

References 62 publications

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“…Auger et al, 2010;Treu et al, 2010;Spiniello et al, 2011;Cappellari et al, 2012Cappellari et al, , 2013Brewer et al, 2012;Dutton et al, 2013;Tortora et al, 2013), though we note that increased mass to light ratios can result from both bottom-light and bottom-heavy IMFs (the former owing to increased numbers of low mass stars, which the latter originating in increased numbers of stellar remnants). Considering both the indirect evidence of potential IMF variations at high-z, as well as observations of presentepoch massive galaxies (which are likely descendants of starbursts at high-z), it is fair to say that the form of the IMF in high-z systems is still a completely open issue.…”

Section: Stellar Imfmentioning

confidence: 82%

Dusty star-forming galaxies at high redshift

2014

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Far-infrared and submillimeter wavelength surveys have now established the important role of dusty, star-forming galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe. The brightest of these galaxies have infrared luminosities in excess of 10 13 L with implied star-formation rates of thousands of solar masses per year. They represent the most intense starbursts in the Universe, yet many are completely optically obscured. Their easy detection at submm wavelengths is due to dust heated by ultraviolet radiation of newly forming stars. When summed up, all of the dusty, star-forming galaxies in the Universe produce an infrared radiation field that has an equal energy density as the direct starlight emission from all galaxies visible at ultraviolet and optical wavelengths. The bulk of this infrared extragalactic background light emanates from galaxies as diverse as gas-rich disks to mergers of intense starbursting galaxies. Major advances in far-infrared instrumentation in recent years, both spacebased and ground-based, has led to the detection of nearly a million DSFGs, yet our understanding of the underlying astrophysics that govern the start and end of the dusty starburst phase is still in nascent stage. This review is aimed at summarizing the current status of DSFG studies, focusing especially on the detailed characterization of the bestunderstood subset (submillimeter galaxies, who were summarized in the last review of this field over a decade ago, Blain et al. 2002), but also the selection and characterization of more recently discovered DSFG populations. We review DSFG population statistics, their physical properties including dust, gas and stellar contents, their environments, and current theoretical models related to the formation and evolution of these galaxies.

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Section: Stellar Imfmentioning

confidence: 82%

Dusty star-forming galaxies at high redshift

2014

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“…There are indications that the light of stars in massive early type galaxies is consistent with populations formed with a bottom-heavy IMF, as given by the analysis of their spectral features (van Dokkum & Conroy 2010Ferreras et al 2013;La Barbera et al 2013;; in other works, the mass-to-light ratio of massive early type galaxies is constrained by using dynamical tools (Cappellari et al 2012;Dutton et al 2012;Tortora et al 2013) or strong gravitational lensing Treu et al 2010). However, these methods present a degeneracy in the sense that a higher ratio of less massive stars implies either a bottom heavy IMF or a top heavy IMF, since massive stars end their lives in short time-scales and contribute to the total emitted light only during star formation events and shortly after.…”

Section: Discussionmentioning

confidence: 99%

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Gargiulo¹,

Cora²,

Padilla³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between [α/Fe] abundance ratios and stellar mass in elliptical galaxies. We implement a new galaxy-wide stellar initial mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in the semi-analytic model SAG and evaluate its impact on the chemical evolution of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct [α/Fe]-stellar mass relation. Massive galaxies reach higher [α/Fe] abundance ratios because they are characterized by more top-heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass and of the slope of the embedded cluster mass function, which are free parameters involved in the TH-IGIMF theory, are found to be as low as 5 M ⊙ and 2, respectively. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass, older galaxies (with formation redshifts 2) are formed in shorter time-scales ( 2 Gyr), thus achieving larger [α/Fe] values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the [α/Fe]-galaxy mass relation, but is responsible for the big dispersion of [α/Fe] abundance ratios at fixed stellar mass. We further test the hyphothesis of a TH-IGIMF in elliptical galaxies by looking into mass-to-light ratios, and luminosity functions. Models with a TH-IGIMF are also favoured by these constraints. In particular, mass-to-light ratios agree with observed values for massive galaxies while being overpredicted for less massive ones; this overprediction is present regardless of the IMF considered.

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“…detailed 2D axisymmetric dynamical models (Cappellari et al 2012), simpler spherical dynamical models (Tortora et al 2013), or through a joint lensing and dynamical analysis of gravitational lenses (Treu et al 2010). The two independent approaches have been shown to achieve a similar trend with velocity dispersion (Tortora et al 2013;Conroy et al 2013). This consolidates the robustness of the IMF-σ trend in local massive ETGs, although caveats and limits of both methods need to be fully understood yet (Smith 2014).…”

Section: Introductionmentioning

confidence: 99%

Lower mass normalization of the stellar initial mass function for dense massive early-type galaxies atz~ 1.4

Gargiulo

Saracco

Longhetti

et al. 2015

A&A

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Aims. This paper aims at understanding whether the normalization of the stellar initial mass function (IMF) of massive galaxies varies with cosmic time and/or with mean stellar mass density Σ = M /(2πR 2 e ). Methods. We have tackled this question by taking advantage of a spectroscopic sample of 18 dense (Σ > 2500 M pc −2 ) massive early-type galaxies (ETGs) that we collected at 1.2 < ∼ z < ∼ 1.6. Each galaxy in the sample was selected in order to have available: i) a high-resolution deep HST-F160W image to visually classify it as an ETG; ii) an accurate velocity dispersion estimate; iii) stellar mass derived through the fit of multiband photometry; and iv) structural parameters (i.e. effective radius R e and Sersic index n) derived in the F160W-band. We have constrained the mass-normalization of the IMF of dense high-z ETGs by comparing the true stellar masses of the ETGs in the sample (M true ) derived through virial theorem, hence IMF independent, with those inferred through the fit of the photometry which assume a reference IMF (M ref ). Adopting the virial estimator as proxy of the true stellar mass, we have implicitly assumed that these systems have zero dark matter. However, recent dynamical analysis of massive local ETGs have shown that the dark matter fraction within R e in dense ETGs is negligible (<5−10%) and simulations of dissipationless mergers of spheroidal galaxies have shown that this fraction decreases going back with time. Accurate dynamical models of local ETGs performed by the ATLAS 3D team have shown that the virial estimator is prone to underestimating or overestimating the total masses. We have considered this, and based on the results of ATLAS 3D we have shown that for dense ETGs the mean value of total masses derived through the virial estimator with a non-homologous virial coefficient and Sersic-R e are perfectly in agreement with the mean value of those derived through more sophisticated dynamical models, although, of course, the estimates show higher uncertainties. Results. Tracing the variation of the parameter Γ = M true /M ref with velocity dispersion σ e , we have found that, on average, dense ETGs at z = 1.4 follow the same IMF-σ e trend of typical local ETGs, but with a lower mass-normalization. The observed lower normalization could be evidence of i) an evolution of the IMF with time or ii) a correlation with Σ. To discriminate between the two possibilities, we have compared the IMF-σ e trend that we have found for high-z dense ETGs with that of local ETGs with similar mean stellar mass density and velocity dispersion and we have found that the IMF of massive dense ETGs does not depend on redshift. The similarity between the IMF-σ e trends observed both in dense high-z and low-z ETGs over 9 Gyr of evolution and their lower massnormalization with respect to the mean value of local ETGs suggests that, independently of formation redshift, the physical conditions which characterized the formation of a dense spheroid on average lead to a mass spectrum of newly formed stars ...

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An Inventory of the Stellar Initial Mass Function in Early-Type Galaxies

Cited by 105 publications

References 62 publications

Dusty star-forming galaxies at high redshift

Dusty star-forming galaxies at high redshift

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

Lower mass normalization of the stellar initial mass function for dense massive early-type galaxies atz~ 1.4

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