scholarly journals Stellar halos around Local Group galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 15-20
Author(s):  
Alan W. McConnachie
Keyword(s):  
Luminosity Function ◽  
Milky Way ◽  
Local Group ◽  
Stellar Populations ◽  
Mass Range ◽  
Stellar Mass ◽  
Intermediate Mass ◽  
Halo Formation ◽  
Stellar Masses

AbstractThe Local Group is now home to 102 known galaxies and candidates, with many new faint galaxies continuing to be discovered. The total stellar mass range spanned by this population covers a factor of close to a billion, from the faintest systems with stellar masses of order a few thousand to the Milky Way and Andromeda, with stellar masses of order 1011M⊙. Here, I discuss the evidence for stellar halos surrounding Local Group galaxies spanning from dwarf scales (with the case of the Andromeda II dwarf spheroidal), though to intermediate mass systems (M33) and finishing with M31. Evidence of extended stellar populations and merging is seen across the luminosity function, indicating that the processes that lead to halo formation are common at all mass scales.

scholarly journals Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations

2020 ◽  
Vol 498 (2) ◽  
pp. 2472-2491 ◽  
Author(s):  
J M Diederik Kruijssen ◽  
Joel L Pfeffer ◽  
Mélanie Chevance ◽  
Ana Bonaca ◽  
Sebastian Trujillo-Gomez ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Mass Range ◽  
Stellar Mass ◽  
Host Galaxies ◽  
Stellar Halo ◽  
Major Merger ◽  
Virial Mass ◽  
Minor Mergers ◽  
Stellar Masses

ABSTRACT Globular clusters (GCs) formed when the Milky Way experienced a phase of rapid assembly. We use the wealth of information contained in the Galactic GC population to quantify the properties of the satellite galaxies from which the Milky Way assembled. To achieve this, we train an artificial neural network on the E-MOSAICS cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies. The network uses the ages, metallicities, and orbital properties of GCs that formed in the same progenitor galaxies to predict the stellar masses and accretion redshifts of these progenitors. We apply the network to Galactic GCs associated with five progenitors: Gaia-Enceladus, the Helmi streams, Sequoia, Sagittarius, and the recently discovered ‘low-energy’ GCs, which provide an excellent match to the predicted properties of the enigmatic galaxy ‘Kraken’. The five galaxies cover a narrow stellar mass range [M⋆ = (0.6–4.6) × 108 M⊙], but have widely different accretion redshifts ($\mbox{$z_{\rm acc}$}=0.57\!-\!2.65$). All accretion events represent minor mergers, but Kraken likely represents the most major merger ever experienced by the Milky Way, with stellar and virial mass ratios of $\mbox{$r_{M_\star }$}=1$:$31^{+34}_{-16}$ and $\mbox{$r_{M_{\rm h}}$}=1$:$7^{+4}_{-2}$, respectively. The progenitors match the z = 0 relation between GC number and halo virial mass, but have elevated specific frequencies, suggesting an evolution with redshift. Even though these progenitors likely were the Milky Way’s most massive accretion events, they contributed a total mass of only log (M⋆, tot/M⊙) = 9.0 ± 0.1, similar to the stellar halo. This implies that the Milky Way grew its stellar mass mostly by in-situ star formation. We conclude by organizing these accretion events into the most detailed reconstruction to date of the Milky Way’s merger tree.

scholarly journals Weighing Milky Way satellites with LISA

2021 ◽  
Vol 502 (1) ◽  
pp. L55-L60
Author(s):  
Valeriya Korol ◽  
Vasily Belokurov ◽  
Christopher J Moore ◽  
Silvia Toonen
Keyword(s):  
Gravitational Waves ◽  
White Dwarf ◽  
Milky Way ◽  
Stellar Populations ◽  
Stellar Mass ◽  
Star Formation History ◽  
Population Synthesis ◽  
White Dwarf Stars ◽  
Order Of Magnitude ◽  
Stellar Masses

ABSTRACT White dwarf stars are a well-established tool for studying Galactic stellar populations. Two white dwarfs in a tight binary system offer us an additional messenger – gravitational waves – for exploring the Milky Way and its immediate surroundings. Gravitational waves produced by double white dwarf (DWD) binaries can be detected by the future Laser Interferometer Space Antenna (LISA). Numerous and widespread DWDs have the potential to probe shapes, masses, and formation histories of the stellar populations in the Galactic neighbourhood. In this work we outline a method for estimating the total stellar mass of Milky Way satellite galaxies based on the number of DWDs detected by LISA. To constrain the mass we perform a Bayesian inference using binary population synthesis models and considering the number of detected DWDs associated with the satellite and the measured distance to the satellite as the only inputs. Based on a fiducial binary population synthesis model we find that for large satellites the stellar masses can be recovered to within (1) a factor 2 if the star formation history (SFH) is known and (2) an order of magnitude when marginalizing over different SFH models. For smaller satellites we can place upper limits on their stellar mass. Gravitational wave observations can provide mass measurements for large satellites that are comparable, and in some cases more precise, than standard electromagnetic observations.

scholarly journals Correlations between H α equivalent width and galaxy properties at z = 0.47: Physical or selection-driven?

2021 ◽  
Vol 503 (4) ◽  
pp. 5115-5133
Author(s):  
A A Khostovan ◽  
S Malhotra ◽  
J E Rhoads ◽  
S Harish ◽  
C Jiang ◽  
...  
Keyword(s):  
Star Formation ◽  
Equivalent Width ◽  
Luminosity Function ◽  
Mass Function ◽  
Stellar Mass ◽  
High Mass ◽  
Selection Effects ◽  
Star Formation Activity ◽  
Low Mass ◽  
Stellar Masses

ABSTRACT The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H α EW strongly anticorrelates with stellar mass as M−0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H α EW intrinsically correlates with stellar mass as W0∝M−0.16 ± 0.03 and decreases by a factor of ∼3 from 107 M⊙ to 1010 M⊙, while not correcting for selection effects steepens the correlation as M−0.25 ± 0.04. We find low-mass H α emitters to be ∼320 times more likely to have rest-frame EW>200 Å compared to high-mass H α emitters. Combining the intrinsic W0–stellar mass correlation with an observed stellar mass function correctly reproduces the observed H α luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W0–stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H α emitters and not a byproduct of selection effects.

scholarly journals POPULATION OF BLACK HOLES IN THE MILKY WAY AND IN THE MAGELLANIC CLOUDS

2013 ◽  
Vol 53 (A) ◽  
pp. 665-670
Author(s):  
Janusz Ziółkowski
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Milky Way ◽  
Stellar Mass ◽  
Magellanic Clouds ◽  
Intermediate Mass ◽  
Different Types ◽  
The Galaxy

In this review, I will briefly discuss the different types of black hole (BH) populations (supermassive, intermediate mass and stellar mass BHs) both in the Galaxy and in the Magellanic Clouds and compare them with each other.

scholarly journals Towards a consistent framework of comparing galaxy mergers in observations and simulations

2020 ◽  
Vol 644 ◽  
pp. A87
Author(s):  
L. Wang ◽  
W. J. Pearson ◽  
V. Rodriguez-Gomez
Keyword(s):  
Mass Range ◽  
Stellar Mass ◽  
Mass Scale ◽  
Mass Dependence ◽  
Deep Convolutional Neural Networks ◽  
Wide Range ◽  
The Galaxy ◽  
Major Merger ◽  
Mass Assembly ◽  
Stellar Masses

Aims. We aim to perform consistent comparisons between observations and simulations on the mass dependence of the galaxy major merger fraction at low redshift over an unprecedentedly wide range of stellar masses (∼109 to 1012 M⊙). Methods. We first carry out forward modelling of ideal synthetic images of major mergers and non-mergers selected from the Next Generation Illustris Simulations (IllustrisTNG) to include major observational effects. We then train deep convolutional neural networks (CNNs) using realistic mock observations of galaxy samples from the simulations. Subsequently, we apply the trained CNNs to real the Kilo-Degree Survey (KiDS) images of galaxies selected from the Galaxy And Mass Assembly (GAMA) survey. Based on the major merger samples, which are detected in a consistent manner in the observations and simulations, we determine the dependence of major merger fraction on stellar mass at z ∼ 0.15 and make comparisons between the two. Results. The detected major merger fraction in the GAMA/KiDS observations has a fairly mild decreasing trend with increasing stellar mass over the mass range 109 M⊙ <  M* <  1011.5 M⊙. There is good agreement in the mass dependence of the major merger fraction in the GAMA/KiDS observations and the IllustrisTNG simulations over 109.5 M⊙ <  M* <  1010.5 M⊙. However, the observations and the simulations show some differences at M* >  1010.5 M⊙, possibly due to the supermassive blackhole feedback in its low-accretion state in the simulations which causes a sharp transition in the quenched fractions at this mass scale. The discrepancy could also be due to the relatively small volume of the simulations and/or differences in how stellar masses are measured in simulations and observations.

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 Eclipsing Binaries as Precise Standard Candles and Distance Indicators

2005 ◽  
Vol 13 ◽  
pp. 454-454
Author(s):  
Jens Viggo Clausen
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Eclipsing Binaries ◽  
Accurate Information ◽  
Direct Distance ◽  
Stellar Masses ◽  
Distance Indicators

Double-lined eclipsing binaries are (still) our main source for accurate information on stellar masses, radii, and luminosities. Also, they offer very direct distance determinations, useful within the Milky Way and for Local Group Galaxies. I will briefly review the methods involved and discuss critically their advantages and limitations. Furthermore, past and recent highlights will be presented.

scholarly journals Breaking down the link between luminous and dark matter in massive galaxies

2010 ◽  
Vol 6 (S277) ◽  
pp. 305-308
Author(s):  
Sébastien Foucaud ◽  
Christopher J. Conselice
Keyword(s):  
Dark Matter ◽  
Total Mass ◽  
Mass Range ◽  
Stellar Mass ◽  
Wide Field ◽  
Mass Ratio ◽  
Massive Galaxies ◽  
Halo Masses ◽  
Stellar Masses ◽  
Baryonic Mass

AbstractWe present a study on the clustering of a stellar mass selected sample of galaxies with stellar masses M* > 1010M⊙ at redshifts 0.4 < z < 2.0, taken from the Palomar Observatory Wide-field Infrared Survey. We examine the clustering properties of these stellar mass selected samples as a function of redshift and stellar mass, and find that galaxies with high stellar masses have a progressively higher clustering strength than galaxies with lower stellar masses. We also find that galaxies within a fixed stellar mass range have a higher clustering strength at higher redshifts. We further estimate the average total masses of the dark matter haloes hosting these stellar-mass selected galaxies. For all galaxies in our sample the stellar-mass-to-total-mass ratio is always lower than the universal baryonic mass fraction and the stellar-mass-to-total-mass ratio is strongly correlated with the halo masses for central galaxies, such that more massive haloes contain a lower fraction of their mass in the form of stars. The remaining baryonic mass is included partially in stars within satellite galaxies in these haloes, and as diffuse hot and warm gas. We also find that, at a fixed stellar mass, the stellar-to-total-mass ratio increases at lower redshifts. This suggests that galaxies at a fixed stellar mass form later in lower mass dark matter haloes, and earlier in massive haloes. We interpret this as a ‘halo downsizing’ effect.

scholarly journals Intermediate-mass black hole growth and feedback in dwarf galaxies at high redshifts

2019 ◽  
Vol 487 (4) ◽  
pp. 5549-5563 ◽  
Author(s):  
Paramita Barai ◽  
Elisabete M de Gouveia Dal Pino
Keyword(s):  
Black Holes ◽  
Star Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Formation Rate ◽  
Mass Range ◽  
Stellar Mass ◽  
Host Galaxies ◽  
Intermediate Mass ◽  
Hydrodynamical Simulations

Abstract Intermediate-mass black holes (IMBHs; masses between $100\rm{\, and \,}10^{6} \, \mathrm{M}_{\odot }$) historically comprise of an elusive population compared to stellar-mass and supermassive black holes (BHs). Recently, IMBHs have started to be observed at the centres of low-mass galaxies. We perform cosmological hydrodynamical simulations of $(2 \, h^{-1} ~ {\rm Mpc})^3$ comoving boxes and investigate the growth and feedback of central IMBHs in dwarf galaxies (DGs). The earliest BHs appear at z ∼ 18–25 and grow thereafter by accreting gas and by merger with other BHs. We find that, starting from $10^{2} \, \mathrm{M}_{\odot }$, it is possible to build up IMBHs of a few$\times 10^{5}\!-\!10^{6} \, \mathrm{M}_{\odot }$ by z = 5, when the BHs are seeded in haloes less massive than $4 \times 10^{7} \, \mathrm{M}_{\odot }$. The BH accretion rates increase with time and reach $\dot{M}_{\rm BH} = (0.2\!-\!0.8) \dot{M}_{\rm Edd}$ for the massive IMBHs by z = 4. The star formation rate density (SFRD) evolution of the DGs (stellar mass $10^{5}\!-\!10^{8} \, \mathrm{M}_{\odot }$) has a peak plateau between z = 4 and 6. Star formation is quenched between z = 9 and 4. The SFRD is reduced by factors up to 3 when the BHs have grown to a few times $10^5 \, \mathrm{M}_{\odot }$. Even in the presence of stronger supernova (SN)-driven mass ejection, the BHs continue to grow up to z ∼ 6, sustained by gas inflows driven by galaxy mergers and interactions in a cosmological environment. Our conclusions, based on numerical simulation results, support the scenario that early feedback from IMBHs in gas-rich DGs at z = 5–8 can potentially solve several anomalies in the DG mass range within the concordance Λ cold dark matter (ΛCDM) cosmological scenario (Silk 2017). Our results suggest that IMBHs at DG centres grow faster than their host galaxies in the early Universe, and the resulting BH feedback turns the DGs and the BHs dormant.

scholarly journals Stellar Populations and Dark Matter in the Milky Way Disk and in Local Group Galaxies

2008 ◽  
Vol 4 (S254) ◽  
pp. 49-60
Author(s):  
Eva K. Grebel
Keyword(s):  
Dark Matter ◽  
Chemical Evolution ◽  
Age Structure ◽  
Milky Way ◽  
Local Group ◽  
Galactic Disk ◽  
Stellar Populations ◽  
Short Overview

AbstractOur knowledge on the age structure, the chemical evolution, and the kinematics of the Galactic disk has grown substantially during the last years. Recent results on the properties of the stellar populations in the Galactic disk are summarized, and ongoing and future surveys and facilities are discussed. A short overview of recent mass estimates for the Milky Way is presented, and a brief summary of some of the key properties of the Galactic companions is given. The coming decade promises major breakthroughs in understanding our Milky Way, its disk, and the role of its satellites.

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