scholarly journals HI in the outskirts of Nearby Spirals

2016 ◽  
Vol 11 (S321) ◽  
pp. 235-237
Author(s):  
Elias Brinks ◽  
António Portas
Keyword(s):  
Spiral Galaxy ◽  
Surface Density ◽  
Column Density ◽  
Large Radius ◽  
Type Function ◽  
Radial Profiles ◽  
Atomic Gas ◽  
Turn Over

AbstractWe analyse nine galaxies taken from the THINGS survey to investigate the H I extent of spiral galaxy disks. We exploit the high spatial and velocity resolution, and the sensitivity of THINGS to investigate where the atomic gas disks end and what might shape their outskirts. We find that the atomic gas surface density across most of the disk is constant at 5 to 10 M⊙ pc−2 and declines at large radius. The shape of the H I distribution can be described by a Sérsic–type function with a slope index n = 0.18 – 0.36. The H I column density at which radial profiles turn over is found to be at too high a level for it to be caused by ionisation by a meta–galactic UV field. Instead we suggest the H I extent is rather set by how galaxy disks form.

scholarly journals Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies

2020 ◽  
Vol 641 ◽  
pp. A70 ◽  
Author(s):  
Cecilia Bacchini ◽  
Filippo Fraternali ◽  
Giuliano Iorio ◽  
Gabriele Pezzulli ◽  
Antonino Marasco ◽  
...  
Keyword(s):  
Star Formation ◽  
Kinetic Energy ◽  
Surface Density ◽  
Neutral Medium ◽  
Molecular Gas ◽  
Driving Mechanism ◽  
Nearby Star ◽  
Star Forming ◽  
Radial Profiles ◽  
Atomic Gas

It is widely known that the gas in galaxy discs is highly turbulent, but there is much debate on which mechanism can energetically maintain this turbulence. Among the possible candidates, supernova (SN) explosions are likely the primary drivers but doubts remain on whether they can be sufficient in regions of moderate star formation activity, in particular in the outer parts of discs. Thus, a number of alternative mechanisms have been proposed. In this paper, we measure the SN efficiency η, namely the fraction of the total SN energy needed to sustain turbulence in galaxies, and verify that SNe can indeed be the sole driving mechanism. The key novelty of our approach is that we take into account the increased turbulence dissipation timescale associated with the flaring in outer regions of gaseous discs. We analyse the distribution and kinematics of HI and CO in ten nearby star-forming galaxies to obtain the radial profiles of the kinetic energy per unit area for both the atomic gas and the molecular gas. We use a theoretical model to reproduce the observed energy with the sum of turbulent energy from SNe, as inferred from the observed star formation rate (SFR) surface density, and the gas thermal energy. For the atomic gas, we explore two extreme cases in which the atomic gas is made either of cold neutral medium or warm neutral medium, and the more realistic scenario with a mixture of the two phases. We find that the observed kinetic energy is remarkably well reproduced by our model across the whole extent of the galactic discs, assuming η constant with the galactocentric radius. Taking into account the uncertainties on the SFR surface density and on the atomic gas phase, we obtain that the median SN efficiencies for our sample of galaxies are ⟨ηatom⟩ = 0.015−0.008+0.018 for the atomic gas and ⟨ηmol⟩ = 0.003−0.002+0.006 for the molecular gas. We conclude that SNe alone can sustain gas turbulence in nearby galaxies with only few percent of their energy and that there is essentially no need for any further source of energy.

scholarly journals H i imaging of dwarf star-forming galaxies: masses, morphologies, and gas deficiencies

2020 ◽  
Vol 498 (4) ◽  
pp. 4745-4789
Author(s):  
S Jaiswal ◽  
A Omar
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Surface Density ◽  
Column Density ◽  
Line Emission ◽  
Scaling Relations ◽  
Dwarf Star ◽  
Star Forming ◽  
Average Value ◽  
Tidal Interactions

ABSTRACT The Giant Meter-wave Radio Telescope observations of the H i 21 cm-line emission from 13 nearby dwarf star-forming galaxies are presented. These galaxies are selected from the catalogues of Wolf−Rayet galaxies having very young (≤10 Myr) star formation. The ranges of star formation rates and stellar masses of the sample galaxies are 0.03–1.7 M⊙ yr−1 and 0.04–22.3 × 108 M⊙, respectively. The H i line emission is detected from 12 galaxies with peak column density >1 × 1021 cm−2. The 3σ H i column density sensitivities per channel width of 7 km s−1 for low (60 arcsec × 60 arcsec) resolution images are in the range 0.8–1.9 × 1019 cm−2. The H i channel images, moment images, global profiles, and mass surface density profiles are presented here. The average value of the peak H i mass surface density is estimated to be ∼2.5 M⊙ pc−2, which is significantly less compared to that in massive spiral galaxies. The scaling relations of $(M_{stars} + M_{\rm H\, I} + M_{\rm He})$versus Mdyn, gas fraction versus MB, $M_{\rm H\, I}$versus Mstars, H i-to-stellar mass ratio versus Mstars, and $M_{\rm H\, I}$versus $D_{\rm H\, I}$for the sample galaxies are estimated. These scaling relations can be used to constraint the key parameters in the galaxy evolution models. These galaxies are residing in group environment with galaxy density up to eight galaxy Mpc−3. An H i mass deficiency (with DEFH i > 0.3) is noticed in majority of galaxies for their optical diameters as compared to galaxies in field environments. Clear signatures of tidal interactions in these galaxies could be inferred using the H i images. Isolated H i clouds without known optical counterparts are seen in the vicinity of several galaxies. H i emission envelope is found to be having an offset from the optical envelope in several galaxies. Consistent with the previous studies on galaxy evolution in group environments, tidal interactions seem to play an important role in triggering recent star formation.

scholarly journals The Molecular Gas Component of Galaxy Disks

2008 ◽  
Vol 4 (S254) ◽  
pp. 307-312
Author(s):  
Leo Blitz
Keyword(s):  
Hydrostatic Pressure ◽  
Surface Density ◽  
Stellar Surface ◽  
Molecular Gas ◽  
Atomic Gas ◽  
Gas Component

AbstractThe molecular gas in galaxy disks shows much more galaxy to galaxy variation than does the atomic gas. Detailed studies show that this variation can be attributed to differences in hydrostatic pressure in the disks due largely to variations in the stellar surface density and the total gas surface density. One prediction of pressure modulated H2 formation is that the location where HI and H2 have equal surface densities occurs at a constant value of the stellar surface density in the disk. Observations confirm this constancy to 40%.

scholarly journals The star formation history of galaxies in 3D: CALIFA perspective

2014 ◽  
Vol 10 (S309) ◽  
pp. 99-104
Author(s):  
R. M. González Delgado ◽  
R. Cid Fernandes ◽  
R. García-Benito ◽  
E. Pérez ◽  
A. L. de Amorim ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Spectral Synthesis ◽  
Stellar Mass ◽  
Star Formation History ◽  
Chemical Enrichment ◽  
Radial Profiles ◽  
Formation History ◽  
The Galaxy ◽  
History Of

AbstractWe resolve spatially the star formation history of 300 nearby galaxies from the CALIFA integral field survey to investigate: a) the radial structure and gradients of the present stellar populations properties as a function of the Hubble type; and b) the role that plays the galaxy stellar mass and stellar mass surface density in governing the star formation history and metallicity enrichment of spheroids and the disks of galaxies. We apply the fossil record method based on spectral synthesis techniques to recover spatially and temporally resolved maps of stellar population properties of spheroids and spirals with galaxy mass from 109 to 7×1011 M⊙. The individual radial profiles of the stellar mass surface density (μ⋆), stellar extinction (AV), luminosity weighted ages (〈logage〉L), and mass weighted metallicity (〈log Z/Z⊙〉M) are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc and Sd). All these properties show negative gradients as a sight of the inside-out growth of massive galaxies. However, the gradients depend on the Hubble type in different ways. For the same galaxy mass, E and S0 galaxies show the largest inner gradients in μ⋆; and Andromeda-like galaxies (Sb with log M⋆ (M⊙) ∼ 11) show the largest inner age and metallicity gradients. In average, spiral galaxies have a stellar metallicity gradient ∼ −0.1 dex per half-light radius, in agreement with the value estimated for the ionized gas oxygen abundance gradient by CALIFA. A global (M⋆-driven) and local (μ⋆-driven) stellar metallicity relation are derived. We find that in disks, the stellar mass surface density regulates the stellar metallicity; in spheroids, the galaxy stellar mass dominates the physics of star formation and chemical enrichment.

scholarly journals The atomic gas in outer disks in semi-analytic models of galaxy formation

2016 ◽  
Vol 11 (S321) ◽  
pp. 131-131
Author(s):  
Jian Fu ◽  
Yu Luo
Keyword(s):  
Galaxy Formation ◽  
Surface Density ◽  
Mass Relation ◽  
Gas Stripping ◽  
Density Region ◽  
Radial Profiles ◽  
Gas Accretion ◽  
Analytic Models ◽  
Gas Component ◽  
Cold Gas

AbstractWe use semi-analytic models of galaxy formation L-Galaxies based on ΛCDM cosmology to study the HI gas component in galaxy outskirts. We adopt the radially-resolved version of the models by Fu et al. (2013), which includes both atomic and molecular gas component in interstellar medium. This model has been recently updated by Luo et al. (2016) to include cold gas stripping in the outer disk regions of the satellite galaxies by ram pressure. In our models, we can perfectly reproduce the HI size-mass relation, which is discovered by Broeils & Rhee (1997) and confirmed by many subsequent observations. In our model, the reason for such tight correlation between HI size and mass is atomic-molecular phase conversion in high gas surface density regions while HI ionization in low gas surface density region, which leads to very narrow distribution of HI mean surface density. The models also reproduce the universal exponential HI radial profiles in galaxy outskirts found by Bluedisk (Wang et al. 2013), which arises from cold gas accretion onto the galaxy disks in exponentially profiles.

scholarly journals Stochastic 2-D Models of Galaxy Disk Evolution. The Galaxy M33

2014 ◽  
Vol 23 (3-4) ◽  
Author(s):  
T. Mineikis ◽  
V. Vansevičius
Keyword(s):  
Star Formation ◽  
Parameter Space ◽  
Surface Density ◽  
Surface Brightness ◽  
Radial Profiles ◽  
The Galaxy ◽  
Galaxy Disk ◽  
Disk Evolution ◽  
Density Surface ◽  
D Model

AbstractWe have developed a fast numerical 2-D model of galaxy disk evolution (resolved along the galaxy radius and azimuth) by adopting a scheme of parameterized stochastic self-propagating star formation. We explore the parameter space of the model and demonstrate its capability to reproduce 1-D radial profiles of the galaxy M33: gas surface density, surface brightness in the

scholarly journals Star Formation Thresholds: The View from Inside the Galaxy

2015 ◽  
Vol 11 (S315) ◽  
pp. 183-190
Author(s):  
James Di Francesco
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Column Density ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Forming ◽  
Gould Belt ◽  
The Galaxy ◽  
Dynamical Properties ◽  
The Relationship

AbstractWe explore the relationship between the total gas surface density and star formation rate surface density, a.k.a., the “Kennicutt-Schmidt relation,” in a Galactic context. Specifically, we probe the origins of thresholds in the behaviour of the K-S relation at 10 M⊙ pc−2 and 100-200 M⊙ pc−2 using images from the Herschel Hi-GAL and Gould Belt surveys. In both cases, pervasive filamentary structures are seen, possibly due to turbulent motions. The Hi-GAL image supports the view that at ~10 M⊙ pc−2 gas becomes molecular, leading to the formation of clouds that harbour star formation. The GBS images suggest the 100-200 M⊙ pc−2 threshold originates from the nature of filaments being stable until a critical column density of ~160 M⊙ pc−2 is reached. Therefore, the transition between non-star-forming and star-forming gas in clouds (and galaxies) may be set universally by the dynamical properties of filaments.

scholarly journals Proto-planetary disks with CARMA: sub-arsecond observations at millimeter wavelengths

2009 ◽  
Vol 5 (H15) ◽  
pp. 738-738
Author(s):  
Isella Andrea ◽  
John M. Carpenter ◽  
Laura Perez ◽  
Anneila I. Sargent
Keyword(s):  
Surface Density ◽  
Angular Resolution ◽  
Spatial Scales ◽  
Radial Profile ◽  
Continuum Emission ◽  
Disk Radius ◽  
Orbital Radius ◽  
Disk Structure ◽  
Millimeter Wavelengths ◽  
Radial Profiles

Using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) we observed several proto-planetary disks in the dust continuum emission at 1.3 and 2.8 mm (Isella et al. 2009a, 2009b). The observations have angular resolution between 0.15 and 0.7 arcsecond, corresponding to spatial scales spanning from about the orbit of Saturn up to about the orbital radius of Pluto. The observed disks are characterized by a variety of radial profiles for the dust density. We observe inner disk clearing as well as smooth density profiles, suggesting that disks may form, or evolve, in different ways. Despite that, we find that the characteristic disk radius is correlated with the stellar age increasing from 20 AU to 100 AU over about 5 Myr. Interpreting our results in terms of the temporal evolution of a viscous α-disk, we estimate that (i) at the beginning of the disk evolution about 60% of the circumstellar material was located inside radii of 25-40 AU, (ii) that disks formed with masses from 0.05 to 0.4 solar masses and (iii) that the viscous timescale at the disk initial radius is about 0.1-0.3 Myr. Viscous disk models tightly link the surface density Σ(R) with the radial profile of the disk viscosity ν(R)∝ Rγ. We find values of γ ranging from -0.8 to 0.8, suggesting that the viscosity dependence on the orbital radius can be very different in the observed disks. We demonstrate that the similarity solution for the surface density for γ < 0 can explain the properties of some “transitional” disks without requiring discontinuities in the disk surface density. In the case of LkCa 15, a smooth distribution of material from few stellar radii to about 240 AU can produce both the observed SED and the spatially resolved continuum emission at millimeter wavelengths. For two sources, RY Tau and DG Tau, we observed the dust emission with a resolution as high as 0.15 arcsecond, which corresponds to a spatial scale of 20 AU at the distance of the two stars. The achieved angular resolution is a factor 2 higher than any existing observation of circumstellar disks at the same wavelengths and enable us to investigate the disk structure with unprecedent details. In particular, we present a first attempt to derive the radial profile of the slope of the dust opacity β. We find mean values of β of 0.5 and 0.7 for DG Tau and RY Tau respectively and we exclude that β may vary by more than ±0.4 between 20-70 AU. This implies that the circumstellar dust has a maximum grain size between 10 μm and few centimeters.

scholarly journals The Building of Galactic Disks: Insights from the Triangulum Spiral Galaxy Messier 33

2006 ◽  
Vol 2 (S235) ◽  
pp. 29-35
Author(s):  
David L. Block ◽  
Ivânio Puerari ◽  
Giovanni G. Fazio ◽  
Alan Stockton ◽  
Gabriela Canalizo ◽  
...  
Keyword(s):  
Spiral Galaxy ◽  
Open Systems ◽  
Galactic Disk ◽  
Carbon Star ◽  
Absorption Bands ◽  
V Band ◽  
Outer Disk ◽  
Radial Profiles ◽  
The Galaxy ◽  
Low Metallicity

AbstractThe Triangulum Spiral Galaxy Messier 33 offers unique insights into the building of a galactic disk. We identify spectacular arcs of intermediate age (0.6 Gyr − 2 Gyr) stars in the low-metallicity outer disk. The northern arc spans ~120 degrees in azimuth and up to 5 arcmin in width. The arcs are located 2-3 disk scale lengths from the galaxy centre (where 1 disk scale length is equivalent to 0.1 degrees in the V-band) and lie precisely where there is a warp in the HI profile of M33. Warps and infall are inextricably linked (Binney, 1992). We present spectroscopy of candidate stars in the outer northern arc, secured using the Keck I telescope in Hawaii. The target stars have estimated visual magnitudes as faint as V~ 25m. Absorption bands of CN are seen in all spectra reported in this review talk, confirming their carbon star status. Also presented are PAH emissivity radial profiles generated from IRAC observations of M33 using the Spitzer Space Telescope. A dramatic change of phase in the m = 2 Fourier component is detected at the domain of the arcs. M33 serves as an excellent example how the disks of spiral galaxies in our Universe are built: as dynamically open systems, growing from the inward, outward.

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