Comparing the Structural Parameters of the Milky Way to Other Spiral Galaxies

The structural parameters of a galaxy can be used to gain insight into its formation and evolution history.In this paper,we strive to compare the Milky Way’s structural parameters to other,primarily edge-on,spiral galaxies in order to determine how our Galaxy measures up to the Local Universe.For our comparison,we use the galaxy structural parameters gathered from a variety of literature sources in the optical and near-infrared wave bands.We compare the scale length,scale height,and disk flatness for both the thin and thick disks,the thick-to-thin disk mass ratio,the bulge-to-total luminosity ratio,and the mean pitch angle of the Milky Way’s spiral arms to those in other galaxies.We conclude that many of the Milky Way’s structural parameters are largely ordinary and typical of spiral galaxies in the Local Universe,though the Galaxy’s thick disk appears to be appreciably thinner and less extended than expected from zoom-in cosmological simulations of Milky Way-mass galaxies with a significant contribution of galaxy mergers involving satellite galaxies.

Low Surface Brightness Galaxies from BASS+MzLS with Machine Learning

From ∼5000 deg^(2) of the combination of the Beijing–Arizona Sky Survey and Mayall z-band Legacy Survey which is also the northern sky region of the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, we selected a sample of 31,825 candidates of low surface brightness galaxies (LSBGs) with the mean effective surface brightness 24.2<μ_(eff.g)<28.8 mag arcsec^(−2) and the half-light radius 2.″5 < r_(eff)<20″ based on the released photometric catalog and the machine learning model. The distribution of the LSBGs is bimodal in the g−r color, indicating the two distinct populations of the blue (g−r< 0.60) and red (g−r> 0.60) LSBGs. The blue LSBGs appear spiral, disk or irregular while the red LSBGs are spheroidal or elliptical and spatially clustered. This trend shows that the color has a strong correlation with galaxy morphology for LSBGs. In the spatial distribution, the blue LSBGs are more uniformly distributed while the red ones are highly clustered, indicating that red LSBGs preferentially populate a denser environment than the blue LSBGs. Besides, both populations have a consistent distribution of ellipticity (median ∈∼ 0.3), half-light radius (median r_(eff) ∼ 4″) and Sérsic index (median n=1), implying the dominance of the full sample by the round and disk galaxies. This sample has definitely extended the studies of LSBGs to a regime of lower surface brightness, fainter magnitude and broader other properties than the previously Sloan Digital Sky Survey-based samples.

Cross-method Analysis of Corotation Radii Data Set for Spiral Galaxies

A corotation radius is a key characteristic of disk galaxies that is essential to determine the angular speed of the spiral structureΩ_p,and therefore understand its nature.In the literature,there are plenty of methods to estimate this value,but do these measurements have any consistency?In this work,we collected a data set of corotation radius measurements for 547 galaxies,300 of which had at least two values.An initial analysis reveals that most objects have rather inconsistent corotation radius positions.Moreover,a significant fraction of galactic disks is distinguished by a large error coverage and almost uniform distribution of measurements.These findings do not have any relation to spiral type,Hubble classification,or presence of a bar.Among other reasons,obtained results could be explained by the transient nature of spirals in a considerable part of galaxies.We have made our collected data sample publicly available,and have demonstrated on one example how it could be useful for future research by investigating a winding time value for a sample of galaxies with possible multiple spiral arm patterns.

Classifying Globular Clusters and Applying them to Estimate the mass of the Milky Way

We combine the kinematics of 159 globular clusters(GCs) provided by the Gaia Early Data Release 3(EDR3) with other observational data to classify the GCs,and to estimate the mass of the Milky Way(MW).We use the agemetallicity relation,integrals of motion,action space and the GC orbits to identify the GCs as either formed in situ(Bulge and Disk) or ex situ(via accretion).We find that 45.3% have formed in situ,while 38.4% may be related to known merger events:Gaia-Sausage-Enceladus,the Sagittarius dwarf galaxy,the Helmi streams,the Sequoia galaxy and the Kraken galaxy.We also further identify three new sub-structures associated with the Gaia-Sausage-Enceladus.The remaining 16.3% of GCs are unrelated to the known mergers and thought to be from small accretion events.We select 46 GCs which have radii 8.0 <r<37.3 kpc and obtain the anisotropy parameter β=0.315_(-0.049)^(+0.055),which is lower than the recent result using the sample of GCs in Gaia Data Release 2,but still in agreement with it by considering the error bar.By using the same sample,we obtain the MW mass inside the outermost GC as M(<37.3 kpc)=0.423_(-0.02)^(+0.02)×10^(12)M_(⊙),and the corresponding M_(200)=1.11_(-0.18)^(+0.25)×10^(12)M_(⊙).The estimated mass is consistent with the results in many recent studies.We also find that the estimated β and mass depend on the selected sample of GCs.However,it is difficult to determine whether a GC fully traces the potential of the MW.

Galaxy properties derived with spectral energy distribution fitting in the Hawaii-Hubble Deep Field-North

We compile multi-wavelength data from ultraviolet to infrared(IR) bands as well as redshift and source-type information, for a large sample of 178 341 sources in the Hawaii-Hubble Deep Field-North field. A total of 145 635 sources among the full sample are classified/treated as galaxies and have redshift information available. We derive physical properties for these sources utilizing the spectral energy distribution fitting code CIGALE that is based on Bayesian analysis. Through various consistency and robustness checks, we find that our stellar-mass and star-formation rate(SFR) estimates are reliable, which is mainly due to two facts. Firstly, we adopt the most up-to-date and accurate redshifts and point spread functionmatched photometry; and secondly, we make sensible parameter choices with the CIGALE code and take into account the influences of mid-IR/far-IR data, star-formation history models, and AGN contribution. We release our catalog of galaxy properties publicly(including, e.g., redshift, stellar mass, SFR, age, metallicity, dust attenuation). It is the largest of its kind in this field and should facilitate future relevant studies on the formation and evolution of galaxies.

Origin and Properties of Strong MgII Quasar Absorption Line Systems

Strong MgII quasar absorption line systems provide us with a useful tool to understand the gas that plays an important role in galaxy formation. In this paper, placing the theories of galaxy formation in a cosmological context, we present semi-analytic models and Monte-Carlo simulations for strong MgII absorbers produced in gaseous galactic haloes and/or galaxy discs. We investigate the redshift path density for the MgII absorption lines and the properties of galaxy/absorber pairs, in particular the anti-correlation between the equivalent width of MgII absorption line and the projected galaxy-to-sightline distance. The simulated result of the mean redshift path density of strong MgII systems is consistent with the observational result. The fraction of strong MgII systems arising from galaxy disks is predicted to be ~ 10% of the total. There exists an anti-correlation between the absorption line equivalent and the projected distance of sightline to galaxy center and galaxy luminosity. We determined that the mean absorbing radius Rabs≈29 h-1 bpc(LB/LB*)0.35. After taking selection effects into consideration, this becomes Rabs ≈38 h-1 bpc(LB/LB*)0.18, which is in good agreement with the observational result. This shows the importance of considering selection effects when comparing models with observations.