THE MILKY WAY TOMOGRAPHY WITH SLOAN DIGITAL SKY SURVEY. V. MAPPING THE DARK MATTER HALO

ABSTRACT We present a machine learning (ML) approach for the prediction of galaxies’ dark matter halo masses which achieves an improved performance over conventional methods. We train three ML algorithms (XGBoost, random forests, and neural network) to predict halo masses using a set of synthetic galaxy catalogues that are built by populating dark matter haloes in N-body simulations with galaxies and that match both the clustering and the joint distributions of properties of galaxies in the Sloan Digital Sky Survey (SDSS). We explore the correlation of different galaxy- and group-related properties with halo mass, and extract the set of nine features that contribute the most to the prediction of halo mass. We find that mass predictions from the ML algorithms are more accurate than those from halo abundance matching (HAM) or dynamical mass estimates (DYN). Since the danger of this approach is that our training data might not accurately represent the real Universe, we explore the effect of testing the model on synthetic catalogues built with different assumptions than the ones used in the training phase. We test a variety of models with different ways of populating dark matter haloes, such as adding velocity bias for satellite galaxies. We determine that, though training and testing on different data can lead to systematic errors in predicted masses, the ML approach still yields substantially better masses than either HAM or DYN. Finally, we apply the trained model to a galaxy and group catalogue from the SDSS DR7 and present the resulting halo masses.

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Modelling the tightest relation between galaxy properties and dark matter halo properties from hydrodynamical simulations of galaxy formation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa620 ◽

2020 ◽

Vol 493 (3) ◽

pp. 4453-4462

Author(s):

Jian-hua He

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Stellar Mass ◽

Sloan Digital Sky Survey ◽

Dark Matter Halo ◽

Strong Interactions ◽

Circular Velocity ◽

Sky Survey ◽

Hydrodynamical Simulations ◽

Robust Prediction

ABSTRACT We investigate how a property of a galaxy correlates most tightly with a property of its host dark matter halo, using state-of-the-art hydrodynamical simulations of galaxy formation: EAGLE, Illustris, and IllustrisTNG. Unlike most of the previous work, our analyses focus on all types of galaxies, including both central and satellite galaxies. We find that the stellar mass of a galaxy at the epoch of the peak circular velocity with an evolution correction gives the tightest such correlation to the peak circular velocity Vpeak of the galaxy’s underling dark matter halo. The evolution of galaxy stellar mass reduces rather than increases scatter in such a relation. We also find that one major source of scatter comes from star stripping due to the strong interactions between galaxies. Even though, we show that the size of scatter predicted by hydrodynamical simulations has a negligible impact on the clustering of dense Vpeak-selected subhalo from simulations, which suggests that even the simplest subhalo abundance matching (SHAM), without scatter and any additional free parameter, can provide a robust prediction of galaxy clustering that can agree impressively well with the observations from the Sloan Digital Sky Survey (SDSS) main galaxy survey.

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Characterizing the abundance, properties, and kinematics of the cool circumgalactic medium of galaxies in absorption with SDSS DR16

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab871 ◽

2021 ◽

Vol 504 (1) ◽

pp. 65-88

Author(s):

Abhijeet Anand ◽

Dylan Nelson ◽

Guinevere Kauffmann

Keyword(s):

Formation Rate ◽

Sloan Digital Sky Survey ◽

Gas Absorption ◽

Dark Matter Halo ◽

Star Forming ◽

Sky Survey ◽

Optical Continuum ◽

Circumgalactic Medium ◽

Emission Line Galaxies ◽

Red Galaxies

ABSTRACT In order to study the circumgalactic medium (CGM) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive S/N criteria. We process ∼ one million quasars in the latest Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and compile a large sample of ∼ 160 000 Mg ii absorbers, together with ∼ 70 000 Fe ii systems, in the redshift range 0.35 < zabs < 2.3. Combining these with the SDSS DR16 spectroscopy of ∼1.1 million luminous red galaxies (LRGs) and ∼200 000 emission line galaxies (ELGs), we investigate the nature of cold gas absorption at 0.5 < z < 1. These large samples allow us to characterize the scale dependence of Mg ii with greater accuracy than in previous work. We find that there is a strong enhancement of Mg ii absorption within ∼50 kpc of ELGs, and the covering fraction within 0.5rvir of ELGs is 2–5 times higher than for LRGs. Beyond 50 kpc, there is a sharp decline in Mg ii for both kinds of galaxies, indicating a transition to the regime where the CGM is tightly linked with the dark matter halo. The Mg ii-covering fraction correlates strongly with stellar mass for LRGs, but weakly for ELGs, where covering fractions increase with star formation rate. Our analysis implies that cool circumgalactic gas has a different physical origin for star-forming versus quiescent galaxies.

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Clustering and Halo Occupation Distribution of Active Galactic Nuclei

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314003937 ◽

2013 ◽

Vol 9 (S304) ◽

pp. 243-243

Author(s):

Takamitsu Miyaji ◽

M. Krumpe ◽

A. Coil ◽

H. Aceves ◽

B. Husemann

Keyword(s):

Cross Correlation ◽

Dynamic Range ◽

Signal To Noise Ratio ◽

Sloan Digital Sky Survey ◽

Dark Matter Halo ◽

Bias Parameter ◽

X Ray ◽

Sky Survey ◽

Galaxy Population ◽

Halo Occupation Distribution

AbstractWe present the results of our series of studies on correlation function and halo occupation distribution of AGNs utilizing data the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) in the redshift range of 0.07<z<0.36. In order to improve the signal-to-noise ratio, we take cross-correlation approach, where cross-correlation functions (CCF) between AGNs and much more numerous AGNs are analyzed. The calculated CCFs are analyzed using the Halo Occupation Distribution (HOD) model, where the CCFs are divided into the term contributed by the AGN-galaxy pairs that reside in one dark matter halo (DMH), (the 1-halo term) and those from two different DMHs (the 2-halo term). The 2-halo term is the indicator of the bias parameter, which is a function of the typical mass of the DMHs in which AGNs reside. The combination of the 1-halo and 2-halo terms gives, not only the typical DMH mass, but also how the AGNs are distributed among the DMHs as a function of mass separately for those at the center of the DMHs and satellites. The main results are as follows: (1) the range of typical mass of the DMHs in various sub-samples of AGNs log (MDMH/h−1MΘ) ~ 12.4–13.4, (2) we found a dependence of the AGN bias parameter on the X-ray luminosity of AGNs, while the optical luminosity dependence is not significant probably due to smaller dynamic range in luminosity for the optically-selected sample, and (3) the growth of the number of AGNs per DMH (N (MDMH)) with MDMH is shallow, or even may be flat, contrary to that of the galaxy population in general, which grows with MDMH proportionally, suggesting a suppression of AGN triggering in denser environment. In order to investigate the origin of the X-ray luminosity dependence, we are also investigating the dependence of clustering on the black hole mass and the Eddington ratio, we also present the results of this investigation.

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Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3814 ◽

2020 ◽

Author(s):

Bogdan C Ciambur ◽

Francesca Fragkoudi ◽

Sergey Khoperskov ◽

Paola Di Matteo ◽

Françoise Combes

Keyword(s):

Dark Matter ◽

Milky Way ◽

Large Fraction ◽

Formation Time ◽

Dark Matter Halo ◽

Barred Galaxies ◽

Pattern Speed ◽

Nearby Galaxies ◽

Dynamical Instabilities ◽

Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

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The constraining effect of gas and the dark matter halo on the vertical stellar distribution of the Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833510 ◽

2018 ◽

Vol 617 ◽

pp. A142 ◽

Cited By ~ 5

Author(s):

S. Sarkar ◽

C. J. Jog

Keyword(s):

Dark Matter ◽

Gravitational Field ◽

Milky Way ◽

Galactic Disk ◽

Outer Region ◽

Hydrogen Gas ◽

Dark Matter Halo ◽

Stellar Disk ◽

Disk Thickness ◽

Vertical Density

We study the vertical stellar distribution of the Milky Way thin disk in detail with particular focus on the outer disk. We treat the galactic disk as a gravitationally coupled, three-component system consisting of stars, atomic hydrogen gas, and molecular hydrogen gas in the gravitational field of the dark matter halo. The self-consistent vertical distribution for stars and gas in such a realistic system is obtained for radii between 4–22 kpc. The inclusion of an additional gravitating component constrains the vertical stellar distribution toward the mid-plane, so that the mid-plane density is higher, the disk thickness is reduced, and the vertical density profile is steeper than in the one-component, isothermal, stars-alone case. We show that the stellar distribution is constrained mainly by the gravitational field of gas and dark matter halo in the inner and the outer Galaxy, respectively. We find that the thickness of the stellar disk (measured as the half-width at half-maximum of the vertical density distribution) increases with radius, flaring steeply beyond R = 17 kpc. The disk thickness is reduced by a factor of 3–4 in the outer Galaxy as a result of the gravitational field of the halo, which may help the disk resist distortion at large radii. The disk would flare even more if the effect of dark matter halo were not taken into account. Thus it is crucially important to include the effect of the dark matter halo when determining the vertical structure and dynamics of a galactic disk in the outer region.

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Is the dark matter halo of the Milky Way flattened?

Astronomy and Astrophysics ◽

10.1051/0004-6361:20065538 ◽

2006 ◽

Vol 461 (1) ◽

pp. 155-169 ◽

Cited By ~ 20

Author(s):

A. Růžička ◽

J. Palouš ◽

C. Theis

Keyword(s):

Dark Matter ◽

Milky Way ◽

Dark Matter Halo

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Void Dynamics

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316010528 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 530-537

Author(s):

Nelson D. Padilla ◽

Dante Paz ◽

Marcelo Lares ◽

Laura Ceccarelli ◽

Diego Garcí a Lambas ◽

...

Keyword(s):

Dark Matter ◽

Correlation Functions ◽

Cross Correlation ◽

Cosmological Parameters ◽

Matter Field ◽

Sloan Digital Sky Survey ◽

Density Profiles ◽

Peculiar Velocities ◽

Sky Survey ◽

Space Data

AbstractCosmic voids are becoming key players in testing the physics of our Universe. Here we concentrate on the abundances and the dynamics of voids as these are among the best candidates to provide information on cosmological parameters. Cai, Padilla & Li (2014) use the abundance of voids to tell apart Hu & Sawicki f(R) models from General Relativity. An interesting result is that even though, as expected, voids in the dark matter field are emptier in f(R) gravity due to the fifth force expelling away from the void centres, this result is reversed when haloes are used to find voids. The abundance of voids in this case becomes even lower in f(R) compared to GR for large voids. Still, the differences are significant and this provides a way to tell apart these models. The velocity field differences between f(R) and GR, on the other hand, are the same for halo voids and for dark matter voids. Paz et al. (2013), concentrate on the velocity profiles around voids. First they show the necessity of four parameters to describe the density profiles around voids given two distinct void populations, voids-in-voids and voids-in-clouds. This profile is used to predict peculiar velocities around voids, and the combination of the latter with void density profiles allows the construction of model void-galaxy cross-correlation functions with redshift space distortions. When these models are tuned to fit the measured correlation functions for voids and galaxies in the Sloan Digital Sky Survey, small voids are found to be of the void-in-cloud type, whereas larger ones are consistent with being void-in-void. This is a novel result that is obtained directly from redshift space data around voids. These profiles can be used to remove systematics on void-galaxy Alcock-Pacinsky tests coming from redshift-space distortions.

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Through the Eyes of the Sloan Digital Sky Survey... ...Probing Deeper into the Milky Way Galaxy

State of the Universe 2008 - Springer Praxis Books ◽

10.1007/978-0-387-73998-4_9 ◽

2008 ◽

pp. 142-149

Author(s):

Timothy Beers

Keyword(s):

Milky Way ◽

Sloan Digital Sky Survey ◽

Milky Way Galaxy ◽

Sky Survey

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