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Register a new userA Simple Model for Global HI Profiles of Galaxies
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Context. Current and future blind surveys for HI generate large catalogs of spectral lines for which automated characterization would be convenient. Aims. A 6-parameter mathematical model for HI galactic spectral lines is described. The aim of the paper is to show that this model is indeed a useful way to characterize such lines. Methods. The model is fitted to spectral lines extracted for the 34 spiral galaxies of the recent high-definition THINGS survey. Three scenarios with different instrumental characteristics are compared. Quantities obtained from the model fits, most importantly line width and total flux, are compared with analog quantities measured in more standard, non-parametric ways. Results. The model is shown to be a good fit to nearly all the THINGS profiles. When extra noise is added to the test spectra, the fits remain consistent; the model-fitting approach is also shown to return superior estimates of linewidth and flux under such conditions.
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HI line widths are typically interpreted as a measure of ISM turbulence, which is potentially driven by star formation. In an effort to better understand the possible connections between line widths and star formation, we have characterized hi{} kinematics in a sample of nearby dwarf galaxies by co-adding line-of-sight spectra after removing the rotational velocity to produce an average, global hi{} line profile. These superprofiles are composed of a central narrow peak (~6-10 km/s) with higher-velocity wings to either side that contain ~10-15% of the total flux. The superprofiles are all very similar, indicating a universal global HI profile for dwarf galaxies. We compare characteristics of the superprofiles to various galaxy properties, such as mass and measures of star formation (SF), with the assumption that the superprofile represents a turbulent peak with energetic wings to either side. We use these quantities to derive average scale heights for the sample galaxies. When comparing to physical properties, we find that the velocity dispersion of the central peak is correlated with $<Sigma_mathrm{HI}>$. The fraction of mass and characteristic velocity of the high velocity wings are correlated with measures of SF, consistent with the picture that SF drives surrounding HI to higher velocities. While gravitational instabilities provide too little energy, the SF in the sample galaxies does provide enough energy through supernovae, with realistic estimates of the coupling efficiency, to produce the observed superprofiles.
Upcoming HI surveys will deliver large datasets, and automated processing using the full 3-D information (two positional dimensions and one spectral dimension) to find and characterize HI objects is imperative. In this context, visualization is an essential tool for enabling qualitative and quantitative human control on an automated source finding and analysis pipeline. We discuss how Visual Analytics, the combination of automated data processing and human reasoning, creativity and intuition, supported by interactive visualization, enables flexible and fast interaction with the 3-D data, helping the astronomer to deal with the analysis of complex sources. 3-D visualization, coupled to modeling, provides additional capabilities helping the discovery and analysis of subtle structures in the 3-D domain. The requirements for a fully interactive visualization tool are: coupled 1-D/2-D/3-D visualization, quantitative and comparative capabilities, combined with supervised semi-automated analysis. Moreover, the source code must have the following characteristics for enabling collaborative work: open, modular, well documented, and well maintained. We review four state of-the-art, 3-D visualization packages assessing their capabilities and feasibility for use in the case of 3-D astronomical data.
We describe development and application of a Global Astrometric Solution (GAS) to the problem of Pan-STARRS1 (PS1) astrometry. Current PS1 astrometry is based on differential astrometric measurements using 2MASS reference stars, thus PS1 astrometry inherits the errors of the 2MASS catalog. The GAS, based on a single, least squares adjustment to approximately 750k grid stars using over 3000 extragalactic objects as reference objects, avoids this catalog-to-catalog propagation of errors to a great extent. The GAS uses a relatively small number of Quasi-Stellar Objects (QSOs, or distant AGN) with very accurate (<1 mas) radio positions, referenced to the ICRF2. These QSOs provide a hard constraint in the global least squares adjustment. Solving such a system provides absolute astrometry for all the stars simultaneously. The concept is much cleaner than conventional astrometry but is not easy to perform for large catalogs. In this paper we describe our method and its application to Pan-STARRS1 data. We show that large-scale systematic errors are easily corrected but our solution residuals for position (~60 mas) are still larger than expected based on simulations (~10 mas). We provide a likely explanation for the reason the small-scale residual errors are not corrected in our solution as would be expected.
We present a modified version of the L-GALAXIES 2020 semi-analytic model of galaxy evolution, which includes significantly increased direct metal enrichment of the circumgalactic medium (CGM) by supernovae (SNe). These more metal-rich outflows do not require increased mass-loading factors, in contrast to some other galaxy evolution models. This modified L-GALAXIES 2020 model is able to simultaneously reproduce the gas-phase metallicity $(Z_{rm g})$ and stellar metallicity $(Z_{*})$ radial profiles observed in nearby disc galaxies by MaNGA and MUSE, as well as the observed mass - metallicity relations for gas and stars at $z=0$ and their evolution back to $zsim{}2-3$. A direct CGM enrichment fraction of $sim{}90%$ for SNe-II is preferred. We find that massive disc galaxies have slightly flatter $Z_{rm g}$ profiles than their lower-mass counterparts in L-GALAXIES 2020, due to more efficient enrichment of their outskirts via inside-out growth and metal-rich accretion. Such a weak, positive correlation between stellar mass and $Z_{rm g}$ profile slope is also seen in our MaNGA-DR15 sample of 571 star-forming disc galaxies. Although, below ${rm log}(M_{*}/{rm M}_{odot})sim{}10.0$ this observational result is strongly dependent on the metallicity diagnostic and morphological selection chosen. In addition, a lowered maximum SN-II progenitor mass of $25{rm M}_{odot}$, reflecting recent theoretical and observational estimates, can also provide a good match to observed metallicity profiles at $z=0$ in L-GALAXIES 2020. However, this model version fails to reproduce an evolution in $Z_{rm g}$ at fixed mass over cosmic time, or the magnesium abundances observed in the intracluster medium (ICM).
We present the Very Large Array survey of Advanced Camera for Surveys Nearby Galaxy Survey Treasury galaxies (VLA-ANGST). VLA-ANGST is a National Radio Astronomy Observatory Large Program consisting of high spectral (0.6-2.6 km/s) and spatial (~6) resolution observations of neutral, atomic hydrogen (HI) emission toward 35 nearby dwarf galaxies from the ANGST survey. ANGST is a systematic HST survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (Dlesssim4 Mpc). VLA-ANGST provides VLA HI observations of the sub-sample of ANGST galaxies with recent star formation that are observable from the northern hemisphere and that were not observed in the The HI Nearby Galaxy Survey (THINGS). The overarching scientific goal of VLA-ANGST is to investigate fundamental characteristics of the neutral interstellar medium (ISM) of dwarf galaxies. Here we describe the VLA observations, the data reduction, and the final VLA-ANGST data products. We present an atlas of the integrated HI maps, the intensity-weighted velocity fields, the second moment maps as a measure for the velocity dispersion of the HI, individual channel maps, and integrated HI spectra for each VLA-ANGST galaxy. We closely follow the observational setup and data reduction of THINGS to achieve comparable sensitivity and angular resolution. A major difference, however, is the high velocity resolution of the VLA-ANGST observations (0.65 and 1.3km/s for the majority of the galaxies). The VLA-ANGST data products are made publicly available at: https://science.nrao.edu/science/surveys/vla-angst. With available star formation histories from resolved stellar populations and lower resolution ancillary observations from the FIR to the UV, VLA-ANGST will enable detailed studies of the relationship between the ISM and star formation in dwarf galaxies on a ~100 pc scale.
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