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Register a new userThe influence of angular momentum and environment on the HI gas of late-type galaxies
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Chandrashekar Murugeshan
Publication date
2020
fields
Physics
and research's language is
English
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We use high-resolution HI data from the WHISP survey to study the HI and angular momentum properties of a sample of 114 late-type galaxies. We explore the specific baryonic angular momentum -- baryonic mass ($j_b - M_b$) relation, and find that an unbroken power law of the form $j_b propto M_b^{0.55 pm 0.02}$ fits the data well, with an intrinsic scatter of $sim 0.13 pm 0.01$ dex. We revisit the relation between the atomic gas fraction, $f_{atm}$, and the integrated atomic stability parameter $q$ (the $f_{atm} - q$ relation), originally introduced by Obreschkow et al., and probe this parameter space by populating it with galaxies from different environments, in order to study the influence of the environment on their $j_b$, $f_{atm}$ and $q$ values. We find evidence that galaxies with close neighbours show a larger intrinsic scatter about the $f_{atm} - q$ relation compared to galaxies without close-neighbours. We also find enhanced SFR among the deviating galaxies with close neighbours. In addition, we use the bulge-to-total (B/T) ratio as a morphology proxy, and find a general trend of decreasing B/T values with increasing disc stability and HI fraction in the $f_{atm} - q$ plane, indicating a fundamental link between mass, specific angular momentum, gas fraction and morphology of galaxies.
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We investigate the origin, the shape, the scatter, and the cosmic evolution in the observed relationship between specific angular momentum $j_star$ and the stellar mass $M_star$ in early-type (ETGs) and late-type galaxies (LTGs). Specifically, we exploit the observed star-formation efficiency and chemical abundance to infer the fraction $f_{rm inf}$ of baryons that infall toward the central regions of galaxies where star formation can occur. We find $f_{rm inf}approx 1$ for LTGs and $approx 0.4$ for ETGs with an uncertainty of about $0.25$ dex, consistent with a biased collapse. By comparing with the locally observed $j_star$ vs. $M_star$ relations for LTGs and ETGs we estimate the fraction $f_j$ of the initial specific angular momentum associated to the infalling gas that is retained in the stellar component: for LTGs we find $f_japprox 1.11^{+0.75}_{-0.44}$, in line with the classic disc formation picture; for ETGs we infer $f_japprox 0.64^{+0.20}_{-0.16}$, that can be traced back to a $z<1$ evolution via dry mergers. We also show that the observed scatter in the $j_{star}$ vs. $M_{star}$ relation for both galaxy types is mainly contributed by the intrinsic dispersion in the spin parameters of the host dark matter halo. The biased collapse plus mergers scenario implies that the specific angular momentum in the stellar components of ETG progenitors at $zsim 2$ is already close to the local values, in pleasing agreement with observations. All in all, we argue such a behavior to be imprinted by nature and not nurtured substantially by the environment.
We use high-resolution ASKAP observations of galaxies in the Eridanus supergroup to study their HI, angular momentum and star formation properties, as part of the WALLABY pre-pilot survey efforts. The Eridanus supergroup is composed of three sub-groups in the process of merging to form a cluster. The main focus of this study is the Eridanus (or NGC 1395) sub-group. The baryonic specific angular momentum - baryonic mass ($j_{mathrm{b}} - M_{mathrm{b}}$) relation for the Eridanus galaxies is observed to be an unbroken power law of the form $j_{mathrm{b}} propto M_{mathrm{b}}^{0.57 pm 0.05}$, with a scatter of $sim 0.10 pm 0.01$ dex, consistent with previous works. We examine the relation between the atomic gas fraction, $f_{mathrm{atm}}$, and the integrated atomic disc stability parameter $q$ (the $f_{mathrm{atm}} - q$ relation), and find that the Eridanus galaxies deviate significantly from the relation owing to environmental processes such as tidal interactions and ram-pressure affecting their HI gas. We find that a majority of the Eridanus galaxies are HI deficient compared to normal star-forming galaxies in the field. We also find that the star formation among the Eridanus galaxies may be suppressed owing to their environment, thus hinting at significant levels of pre-processing within the Eridanus sub-group, even before the galaxies have entered a cluster-like environment.
We present an empirical method to measure the halo mass function (HMF) of galaxies. We determine the relation between the hi line-width from single-dish observations and the dark matter halo mass ($M_{200}$) inferred from rotation curve fits in the SPARC database, then we apply this relation to galaxies from the hi Parkes All Sky Survey (HIPASS) to derive the HMF. This empirical HMF is well fit by a Schecther function, and matches that expected in $Lambda$CDM over the range $10^{10.5} < M_{200} < 10^{12};mathrm{M}_{odot}$. More massive halos must be poor in neutral gas to maintain consistency with the power law predicted by $Lambda$CDM. We detect no discrepancy at low masses. The lowest halo mass probed by HIPASS, however, is just greater than the mass scale where the Local Group missing satellite problem sets in. The integrated mass density associated with the dark matter halos of hi-detected galaxies sums to $Omega_{rm m,gal} approx 0.03$ over the probed mass range.
In this paper we investigate whether the stellar initial mass function of early-type galaxies depends on their host environment. To this purpose, we have selected a sample of early-type galaxies from the SPIDER catalogue, characterized their environment through the group catalogue of Wang et al. and used their optical SDSS spectra to constrain the IMF slope, through the analysis of IMF-sensitive spectral indices. To reach a high enough signal-to-noise ratio, we have stacked spectra in velocity dispersion ($sigma_0$) bins, on top of separating the sample by galaxy hierarchy and host halo mass, as proxies for galaxy environment. In order to constrain the IMF, we have compared observed line strengths to predictions of MIUSCAT/EMILES synthetic stellar population models, with varying age, metallicity, and bimodal (low-mass tapered) IMF slope ($rm Gamma_b$). Consistent with previous studies, we find that $rm Gamma_b$ increases with $sigma_0$, becoming bottom-heavy (i.e. an excess of low-mass stars with respect to the Milky-Way-like IMF) at high $sigma_0$. We find that this result is robust against the set of isochrones used in the stellar population models, as well as the way the effect of elemental abundance ratios is taken into account. We thus conclude that it is possible to use currently state-of-the-art stellar population models and intermediate resolution spectra to consistently probe IMF variations. For the first time, we show that there is no dependence of $Gamma_b$ on environment or galaxy hierarchy, as measured within the $3$ SDSS fibre, thus leaving the IMF as an intrinsic galaxy property, possibly set already at high redshift.
We study the relationship between the H{sc i} specific angular momentum (j$_{rm g}$) and the H{sc i} mass (M$_{rm g}$) for a sample of galaxies with well measured H{sc i} rotation curves. We find that the relation is well described by an unbroken power law jg $propto$ mg$^{alpha}$ over the entire mass range (10$^{7}$-10$^{10.5}$ M$_{odot}$), with $alpha = 0.89 pm 0.05$ (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H{sc i} disks in a marginally stable state. The slope we observe is also significantly different from both the $j propto M^{2/3}$ relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disk galaxies. Our sample includes two H{sc i}-bearing ultra diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H{sc i} disks which are found to have significantly higher angular momentum than expected from the power law relation. The H{sc i} disks of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar disks, consistent with the gas being recently accreted. We speculate that late stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations.
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