scholarly journals Survey of gravitationally-lensed objects in HSC imaging (SuGOHI)

2019 ◽  
Vol 630 ◽  
pp. A71 ◽  
Author(s):  
Alessandro Sonnenfeld ◽  
Anton T. Jaelani ◽  
James Chan ◽  
Anupreeta More ◽  
Sherry H. Suyu ◽  
...  
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Mass Function ◽  
Initial Mass Function ◽  
Dark Matter Halo ◽  
Open Problems ◽  
Massive Galaxies ◽  
Spatially Resolved ◽  
Stellar Masses ◽  
The Imf

Context. The determination of the stellar initial mass function (IMF) of massive galaxies is one of the open problems in cosmology. Strong gravitational lensing is one of the few methods that allow us to constrain the IMF outside of the Local Group. Aims. The goal of this study is to statistically constrain the distribution in the IMF mismatch parameter, defined as the ratio between the true stellar mass of a galaxy and that inferred assuming a reference IMF, of massive galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) constant mass (CMASS) sample. Methods. We took 23 strong lenses drawn from the CMASS sample, measured their Einstein radii and stellar masses using multi-band photometry from the Hyper Suprime-Cam survey, then fitted a model distribution for the IMF mismatch parameter and dark matter halo mass to the whole sample. We used a prior on halo mass from weak lensing measurements and accounted for strong lensing selection effects in our model. Results. Assuming a Navarro Frenk and White density profile for the dark matter distribution, we infer a value μIMF = −0.04 ± 0.11 for the average base-10 logarithm of the IMF mismatch parameter, defined with respect to a Chabrier IMF. A Salpeter IMF is in tension with our measurements. Conclusions. Our results are consistent with a scenario in which the region of massive galaxies where the IMF normalisation is significantly heavier than that of the Milky Way is much smaller than the scales 5 − 10 kpc probed by the Einstein radius of the lenses in our sample, as recent spatially-resolved studies of the IMF in massive galaxies suggest.

scholarly journals Do ultracompact dwarf galaxies form monolithically or as merged star cluster complexes?

2021 ◽  
Vol 502 (4) ◽  
pp. 5185-5199
Author(s):  
Hamidreza Mahani ◽  
Akram Hasani Zonoozi ◽  
Hosein Haghi ◽  
Tereza Jeřábková ◽  
Pavel Kroupa ◽  
...  
Keyword(s):  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Mass Function ◽  
Star Cluster ◽  
Initial Mass Function ◽  
Central Mass ◽  
Cluster Complexes ◽  
V Band ◽  
Stellar Masses ◽  
The Imf

ABSTRACT Some ultracompact dwarf galaxies (UCDs) have elevated observed dynamical V-band mass-to-light (M/LV) ratios with respect to what is expected from their stellar populations assuming a canonical initial mass function (IMF). Observations have also revealed the presence of a compact dark object in the centres of several UCDs, having a mass of a few to 15 per cent of the present-day stellar mass of the UCD. This central mass concentration has typically been interpreted as a supermassive black hole, but can in principle also be a subcluster of stellar remnants. We explore the following two formation scenarios of UCDs: (i) monolithic collapse and (ii) mergers of star clusters in cluster complexes as are observed in massively starbursting regions. We explore the physical properties of the UCDs at different evolutionary stages assuming different initial stellar masses of the UCDs and the IMF being either universal or changing systematically with metallicity and density according to the integrated Galactic IMF theory. While the observed elevated M/LV ratios of the UCDs cannot be reproduced if the IMF is invariant and universal, the empirically derived IMF that varies systematically with density and metallicity shows agreement with the observations. Incorporating the UCD-mass-dependent retention fraction of dark remnants improves this agreement. In addition, we apply the results of N-body simulations to young UCDs and show that the same initial conditions describing the observed M/LV ratios reproduce the observed relation between the half-mass radii and the present-day masses of the UCDs. The findings thus suggest that the majority of UCDs that have elevated M/LV ratios could have formed monolithically with significant remnant-mass components that are centrally concentrated, while those with small M/LV values may be merged star cluster complexes.

The IMF-SFH connection in massive early-type galaxies

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
I. Ferreras ◽  
C. Weidner ◽  
A. Vazdekis ◽  
F. La Barbera
Keyword(s):  
Age Distribution ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Population Synthesis ◽  
Early Type ◽  
Massive Galaxies ◽  
Stellar Initial Mass Function ◽  
The Many ◽  
The Imf

The stellar initial mass function (IMF) is one of the fundamental pillars in studies of stellar populations. It is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., Salpeter 1955; Kroupa 2001; Chabrier 2003). However, for the vast majority of cases, stars are not resolved in galaxies. Therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including IMF, age distribution, and chemical composition. The overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard IMF choices, made this issue a relatively unimportant one for a number of years. However, improved models and observations have opened the door to constraints on the IMF in unresolved stellar populations via gravity-sensitive spectral features. At present, there is significant evidence of a non-universal IMF in early-type galaxies (ETGs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van Dokkum & Conroy 2010; Ferreras et al. 2013; La Barbera et al. 2013). Dynamical and strong-lensing constraints of the stellar M/L in similar systems give similar results, with heavier M/L in the most massive ETGs (see, e.g., Cappellari et al. 2012; Posacki et al. 2015). Although the interpretation of the results is still open to discussion (e.g., Smith 2014; La Barbera 2015), one should consider the consequences of such a bottom-heavy IMF in massive galaxies.

scholarly journals Stellar velocity dispersion and initial mass function gradients in dissipationless galaxy mergers

2020 ◽  
Vol 499 (1) ◽  
pp. 559-572
Author(s):  
Carlo Nipoti ◽  
Carlo Cannarozzo ◽  
Francesco Calura ◽  
Alessandro Sonnenfeld ◽  
Tommaso Treu
Keyword(s):  
Velocity Dispersion ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Galaxy Mergers ◽  
Orbital Parameters ◽  
Spatially Resolved ◽  
Stellar Velocity ◽  
Stellar Initial Mass Function ◽  
The Imf

ABSTRACT The stellar initial mass function (IMF) is believed to be non-universal among early-type galaxies (ETGs). Parametrizing the IMF with the so-called IMF mismatch parameter αIMF, which is a measure of the stellar mass-to-light ratio of an ensemble of stars and thus of the ‘heaviness’ of its IMF, one finds that for ETGs αe (i.e. αIMF integrated within the effective radius Re) increases with σe (the line-of-sight velocity dispersion σlos integrated within Re) and that, within the same ETG, αIMF tends to decrease outwards. We study the effect of dissipationless (dry) mergers on the distribution of the IMF mismatch parameter αIMF in ETGs using the results of binary major and minor merging simulations. We find that dry mergers tend to make the αIMF profiles of ETGs shallower, but do not alter significantly the shape of the distributions in the spatially resolved σlos–αIMF space. Individual galaxies undergoing dry mergers tend to decrease their αe, due to erosion of αIMF gradients and mixing with stellar populations with lighter IMF. Their σe can either decrease or increase, depending on the merging orbital parameters and mass ratio, but tends to decrease for cosmologically motivated merging histories. The αe–σe relation can vary with redshift as a consequence of the evolution of individual ETGs: based on a simple dry-merging model, ETGs of given σe are expected to have higher αe at higher redshift, unless the accreted satellites are so diffuse that they contribute negligibly to the inner stellar distribution of the merger remnant.

scholarly journals Initial Mass Function for Massive Galaxies at z ~ 1

2014 ◽  
Vol 10 (S311) ◽  
pp. 136-139
Author(s):  
Shravan Shetty ◽  
Michele Cappellari
Keyword(s):  
Dark Matter ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Population Modelling ◽  
Full Spectrum ◽  
Massive Galaxies ◽  
Matching Technique ◽  
Stellar Initial Mass Function ◽  
Spectrum Fitting

AbstractWe present the results on the stellar Initial Mass Function (IMF) normalisation of 68 massive (M* = 1011 - 1012M⋖) Early-Type Galaxies (ETGs) at redshift of ~1. This was achieved by deriving the stellar Mass-to-Light ratio (M/L) of the galaxies through axis-symmetric dynamical modelling and comparing it to the same derived via stellar population modelling through full spectrum fitting. The study also employs an Abundance Matching technique to account for the dark matter within the galaxies. The results demonstrate that massive ETGs at high redshifts on average have a Salpeter-like IMF normalisation, while providing observational evidence supporting previous predictions of low dark matter fraction in the inner regions (<1Re) of galaxies at higher redshift.

scholarly journals A systematic search for galaxy proto-cluster cores at z ∼ 2

2019 ◽  
Vol 15 (S359) ◽  
pp. 166-167
Author(s):  
Makoto Ando ◽  
Kazuhiro Shimasaku ◽  
Rieko Momose
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Clustering Analysis ◽  
Mass Function ◽  
Stellar Mass ◽  
Dark Matter Halo ◽  
Massive Galaxies ◽  
The Galaxy ◽  
Mass Assembly ◽  
Cluster Cores

AbstractA proto-cluster core is the most massive dark matter halo (DMH) in a given proto-cluster. To reveal the galaxy formation in core regions, we search for proto-cluster cores at z ˜ 2 in ˜1.5deg2 of the COSMOS field. Using pairs of massive galaxies (log (M*/Mʘ) ≥ 11) as tracers of cores, we find 75 candidate cores. A clustering analysis and the extended Press-Schechter model show that their descendant mass at z = 0 is consistent with Fornax-like or Virgo-like clusters. Moreover, using the IllustrisTNG simulation, we confirm that pairs of massive galaxies are good tracers of DMHs massive enough to be regarded as proto-cluster cores. We then derive the stellar mass function and the quiescent fraction for member galaxies of the 75 candidate cores. We find that stellar mass assembly and quenching are accelerated as early as z ˜ 2 in proto-cluster cores.

scholarly journals Massive Elliptical Galaxies: BH Scouring or a Bottom-Heavy IMF?

2014 ◽  
Vol 10 (S311) ◽  
pp. 36-39
Author(s):  
Jens Thomas ◽  
Roberto Saglia ◽  
Ralf Bender ◽  
Peter Erwin ◽  
Maximilian Fabricius
Keyword(s):  
Dark Matter ◽  
Power Law ◽  
Milky Way ◽  
Elliptical Galaxies ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Early Type ◽  
Stellar Masses ◽  
Kinematical Data ◽  
The Imf

AbstractWe present indirect constraints on the stellar initial-mass-function (IMF) in nine massive elliptical galaxies with σ ≈ 300 km/s, via a comparison of dynamical and stellar-population based stellar masses. We use adaptive-optics assisted, high resolution kinematical data from the SINFONI Search for Supermassive Black Holes that allow us to constrain the dynamical stellar mass-to-light ratio in the very centre of each galaxy. Hence we measure the IMF in a galaxy region where the stellar mass dominates over dark matter, minimising any potential degeneracy between the two mass components. In six of our galaxies – those which have depleted stellar cores – we find an IMF consistent with the one measured in the Milky-Way via direct star counts. The three remaining, power-law galaxies have instead stellar masses about a factor of two times larger than expected from a Milky-Way type IMF, indicating either a more bottom-heavy IMF (like, e.g., the Salpeter IMF) or a dark-matter distribution that is degenerate with the stellar mass down to the very centres of these galaxies. The bottom-light IMF in our core galaxies is surprising in view of previous studies that suggested a systematic IMF variation where early-type galaxies with σ ≈ 300 km/s have a Salpeter or even more dwarf-dominated IMF. Core galaxies are particularly important since their unique central orbital structure offers an independent crosscheck for the dynamical models. Our models with a bottom-light IMF are consistent with the distribution of orbits predicted by SMBH-binary core-formation models. This indicates that spatially well resolved central kinematical data are important for determining unbiased dynamical stellar mass-to-light ratios. Our results imply either that the IMF in massive galaxies varies over a wider range than previously anticipated, and is not the same in core and power-law ellipticals, or else that there are systematic variations in the distribution of dark matter among massive early-type galaxies.

scholarly journals Abundance matching tested on small scales with galaxy dynamics

2020 ◽  
Vol 496 (1) ◽  
pp. L101-L105
Author(s):  
Andrea V Macciò ◽  
Stéphane Courteau ◽  
Nathalie N-Q Ouellette ◽  
Aaron A Dutton
Keyword(s):  
Dark Matter ◽  
Theoretical Models ◽  
Mass Function ◽  
Virgo Cluster ◽  
Initial Mass Function ◽  
Mass Relation ◽  
Cluster Galaxies ◽  
Galaxy Dynamics ◽  
Hydrodynamical Simulations ◽  
Stellar Masses

Abstract We present a comprehensive test of the relation between stellar and total masses in galaxies as predicted by popular models based on abundance matching (AM) techniques. We use the ‘Spectroscopy and H-band Imaging of Virgo cluster galaxies’ (SHIVir) survey with photometric and dynamical profiles for 190 Virgo cluster galaxies to establish a relation between the stellar and dynamical masses measured within the isophotal radius r23.5. Various dark matter and galaxy scaling relations are combined with results from the NIHAO (Numerical Investigation of Hundred Astrophysical Objects) suite of hydrodynamical simulations to recast AM predictions in terms of these observed quantities. Our results are quite insensitive to the exact choice of dark matter profile and halo response to baryon collapse. We find that theoretical models reproduce the slope and normalization of the observed stellar-to-halo mass relation (SHMR) over more than three orders of magnitude in stellar mass (108 &lt; M*/M⊙ &lt; 2 × 1011). However, the scatter of the observed SHMR exceeds that of AM predictions by a factor of ∼5. For systems with stellar masses exceeding 5 × 1010 M⊙, AM overpredicts the observed stellar masses for a given dynamical mass. The latter offset may support previous indications of a different stellar initial mass function in these massive galaxies. Overall, our results support the validity of AM predictions on a wide dynamical range.

Evidence for Initial Mass Function Variation in Massive Early-Type Galaxies

2020 ◽  
Vol 58 (1) ◽  
pp. 577-615 ◽  
Author(s):  
Russell J. Smith
Keyword(s):  
Gravitational Lensing ◽  
High Redshift ◽  
Mass Function ◽  
Spectroscopic Studies ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Early Type ◽  
Stellar Component ◽  
The Imf

The initial mass function (IMF), describing the distribution of birth masses of stars, plays a pivotal role in establishing the observable properties of galaxies. This article reviews the evidence for variation in the IMF of massive early-type galaxies (ETGs), especially from spectroscopic studies and from dynamical and gravitational lensing measurements over the past decade. The principal conclusions are as follows: ▪  The spectra of massive ETGs depart from the predictions of models with Milky Way–like IMFs in a way that is best reproduced by assuming a steeper (bottom-heavy) IMF below ∼1 M⊙. ▪  Lensing and dynamical models, assuming a constant mass-to-light ratio for the stellar component, infer heavy IMFs, superficially supporting the result from spectra. ▪  The spectroscopic signal exhibits a steep gradient, however, and may be confined to the innermost region with scales ≲2 kpc; such internal variation in the stellar mass-to-light ratio would invalidate a key assumption of most dynamics and lensing studies. ▪  For masses above the main sequence turnoff in ancient populations (≳1 M⊙), there is little evidence for a steeper IMF in massive ETGs or their high-redshift progenitors; rather, a slightly shallower slope is preferred in this regime from several different arguments. ▪  Steep internal gradients may be responsible for some of the apparent discrepancies between different methods and also point to the cause of the IMF variation being restricted to conditions specific to the in situ formation phase of ETG cores.

scholarly journals The normalization and slope of the dark matter (sub-)halo mass function on sub-galactic scales

2020 ◽  
Vol 493 (1) ◽  
pp. 1268-1276
Author(s):  
Andrew J Benson
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Mass Range ◽  
Mass Function ◽  
Matter Content ◽  
Dark Matter Halo ◽  
Halo Masses ◽  
Near Future ◽  
Mass Functions

ABSTRACT Simulations of cold dark matter make robust predictions about the slope and normalization of the dark matter halo and subhalo mass functions on small scales. Recent observational advances utilizing strong gravitational lensing have demonstrated the ability of this technique to place constraints on these quantities on subgalactic scales corresponding to dark matter halo masses of 106–$10^9\, \mathrm{M}_\odot$. On these scales the physics of baryons, which make up around 17 per cent of the matter content of the Universe but which are not included in pure dark matter N-body simulations, are expected to affect the growth of structure and the collapse of dark matter haloes. In this work, we develop a semi-analytic model to predict the amplitude and slope of the dark matter halo and subhalo mass functions on subgalactic scales in the presence of baryons. We find that the halo mass function is suppressed by up to 25 per cent, and the slope is modified, ranging from −1.916 to −1.868 in this mass range. These results are consistent with current measurements, but differ sufficiently from the expectations for a dark matter only universe that it may be testable in the near future.

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