ABSTRACT We present a study of the vertical structure of the gaseous and stellar disks in a sample of edge-on galaxies (NGC 4157, 4565, and 5907) using BIMA/CARMA , VLA Hi, and Spitzer 3.6 m data. In ...order to take into account projection effects when we measure the disk thickness as a function of radius, we first obtain the inclination by modeling the radio data. Using the measurement of the disk thicknesses and the derived radial profiles of gas and stars, we estimate the corresponding volume densities and vertical velocity dispersions. Both stellar and gas disks have smoothly varying scale heights and velocity dispersions, contrary to assumptions of previous studies. Using the velocity dispersions, we find that the gravitational instability parameter Q follows a fairly uniform profile with radius and is across the star-forming disk. The star formation law has a slope that is significantly different from those found in more face-on galaxy studies, both in deprojected and pixel-by-pixel plots. Midplane gas pressure based on the varying scale heights and velocity dispersions appears to roughly hold a power-law correlation with the midplane volume density ratio.
We analyze images of BIMA 12CO (J = 1 -> 0) , Very Large Array H I, and Spitzer 3.6 and 24 Delta *mm emission toward the edge-on galaxy NGC 891 and derive the radial and vertical distributions of gas ...and the radial distributions of stellar mass and recent star formation. We describe our method of deriving radial profiles for edge-on galaxies, assuming circular motion, and verify basic relationships between star formation rate (SFR) and gas and stellar content, and between the molecular-to-atomic ratio and hydrostatic midplane pressure that have been found in other galaxy samples. The Schmidt law index we find for the total gas (H2 + H I) is 0.85 ? 0.55, but the Schmidt law provides a poor description of the SFR in comparison to a model that includes the influence of the stellar disk. Using our measurements of the thickness of the gas disk and the assumption of hydrostatic equilibrium, we estimate volume densities and pressures as a function of radius and height in order to test the importance of pressure in controlling the ratio. The gas pressure in two dimensions P(r, z) using constant velocity dispersion does not seem to correlate with the ratio, but the pressure using varying velocity dispersion appears to correlate with the ratio. We test the importance of gravitational instability in determining the sites of massive star formation and find that the Q parameter using a radially varying gas velocity dispersion is consistent with self-regulation (Q ~ 1) over a large part of the disk.
Abstract
We observe the almost edge-on (
i
∼ 90°) galaxy NGC 4302 using the Atacama Large Millimeter/submillimeter Array (CO) and Very Large Array (H
i
) to measure the gas disk thickness for ...investigating the volumetric star formation law (SFL). The recent star formation rate (SFR) is estimated based on a linear combination of IR 24
μ
m and H
α
emissions. The measured scale heights of CO and H
i
increase significantly with radius. Using the scale heights along with the vertically integrated surface densities, we derive the midplane volume densities of the gas (
ρ
H I
,
ρ
H
2
, and
ρ
gas
=
ρ
H I
+
ρ
H
2
) and the SFR (
ρ
SFR
) and compare the volumetric SFL (
ρ
SFR
∝
ρ
gas
n
) with the vertically integrated SFL (Σ
SFR
∝ Σ
gas
N
). We find tight power-law correlations between the SFR and the gas (H
i
, H
2
, and the total gas) in both volume and surface densities. The power-law indices of the total gas and H
i
for the volumetric SFL are noticeably smaller than the indices for the vertically integrated SFL while the H
2
indices for both cases are similar to each other. In terms of the star formation efficiency (SFE), we find that the molecular and total gas SFEs are roughly constant, while the atomic SFE is clearly decreasing with radius in both cases.
ABSTRACT
We measure the gas disc thicknesses of the edge-on galaxy NGC 4013 and the less edge-on galaxies (NGC 4157 and 5907) using CO (CARMA/OVRO) and/or H i (EVLA) observations. We also estimate ...the scale heights of stars and/or the star formation rate (SFR) for our sample of five galaxies using Spitzer IR data (3.6 and 24 µm). We derive the average volume densities of the gas and the SFR using the measured scale heights along with radial surface density profiles. Using the volume density that is more physically relevant to the SFR than the surface density, we investigate the existence of a volumetric star formation law (SFL), how the volumetric SFL is different from the surface-density SFL, and how the gas pressure regulates the SFR based on our galaxy sample. We find that the volumetric and surface SFLs in terms of the total gas have significantly different slopes, while the volumetric and surface SFLs in terms of the molecular gas do not show any noticeable difference. The volumetric SFL for the total gas has a flatter power-law slope of 1.26 with a smaller scatter of 0.19 dex compared to the slope (2.05) and the scatter (0.25 dex) of the surface SFL. The molecular gas SFLs have similar slopes of 0.78 (volume density) and 0.77 (surface density) with similar rms scatters. We show that the interstellar gas pressure is strongly correlated with the SFR but find no significant difference between the correlations based on the volume and surface densities.
In order to quantify the relationship between gas accretion and star formation, we analyse a sample of 29 nearby galaxies from the WHISP survey which contains galaxies with and without evidence for ...recent gas accretion. We compare combined radial profiles of far-UV (GALEX) and IR 24 ...m (Spitzer) characterizing distributions of recent star formation with radial profiles of CO (IRAM, BIMA, or CARMA) and H i (WSRT) tracing molecular and atomic gas contents to examine star formation efficiencies in symmetric (quiescent), asymmetric (accreting), and interacting (tidally disturbed) galaxies. In addition, we investigate the relationship between star formation rate and H i in the outer discs for the three groups of galaxies. We confirm the general relationship between gas surface density and star formation surface density, but do not find a significant difference between the three groups of galaxies. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to ...the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy’s large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850
μ
m. We also have created a method to predict the CO(
J
= 3–2) line flux across M31, which contaminates the 850
μ
m band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed.
We present a time series of synoptic images of the linearly polarized v = 1, J = 1-0 SiO maser emission toward the Mira variable, TX Cam. These data comprise 43 individual epochs at an approximate ...biweekly sampling over an optical pulsation phase range of = 0.68 to = 1.82. The images have an angular resolution of ~500 is a subset of as and were obtained using the Very Long Baseline Array (VLBA), operating in the 43 GHz band in spectral-line, polarization mode. We have previously published the total intensity time series for this pulsation phase range; this paper serves to present the linearly polarized image sequence and an associated animation representing the evolution of the linear polarization morphology over time. We find a predominantly tangential polarization morphology, a high degree of persistence in linear polarization properties over individual component lifetimes, and stronger linear polarization in the inner projected shell than at larger projected shell radii. We present an initial polarization proper motion analysis examining the possible dynamical influence of magnetic fields in component motions in the extended atmospheres of late-type, evolved stars.
We observe the almost edge-on (i \(\sim\) 90 degrees) galaxy NGC 4302 using ALMA (CO) and VLA (H I) to measure the gas disk thickness for investigating the volumetric star formation law (SFL). The ...recent star formation rate (SFR) is estimated based on a linear combination of IR 24 micron and H\(\alpha\) emissions. The measured scale heights of CO and H I increase significantly with radius. Using the scale heights along with the vertically integrated surface densities, we derive the mid-plane volume densities of the gas (\(\rho_{\rm HI}\), \(\rho_{\rm H_2}\), and \(\rho_{\rm gas}\) = \(\rho_{\rm HI}\)+\(\rho_{\rm H_2}\)) and the SFR (\(\rho_{\rm SFR}\)) and compare the volumetric SFL (\(\rho_{\rm SFR} \propto \rho_{\rm gas}^n\)) with the vertically integrated SFL (\(\Sigma_{\rm SFR} \propto \Sigma_{\rm gas}^N\)). We find tight power-law correlations between the SFR and the gas (H I, H\(_2\), and the total gas) in both volume and surface densities. The power-law indices of the total gas and H I for the volumetric SFL are noticeably smaller than the indices for the vertically integrated SFL while the H\(_2\) indices for both cases are similar to each other. In terms of the star formation efficiency (SFE), we find that the molecular and total gas SFEs are roughly constant, while the atomic SFE is clearly decreasing with radius in both cases.
We measure the gas disc thicknesses of the edge-on galaxy NGC 4013 and the less edge-on galaxies (NGC 4157 and 5907) using CO (CARMA/OVRO) and/or HI (EVLA) observations. We also estimate the scale ...heights of stars and/or the star formation rate (SFR) for our sample of five galaxies using Spitzer IR data (3.6 \(\mu\)m and 24 \(\mu\)m). We derive the average volume densities of the gas and the SFR using the measured scale heights along with radial surface density profiles. Using the volume density that is more physically relevant to the SFR than the surface density, we investigate the existence of a volumetric star formation law (SFL), how the volumetric SFL is different from the surface-density SFL, and how the gas pressure regulates the SFR based on our galaxy sample. We find that the volumetric and surface SFLs in terms of the total gas have significantly different slopes, while the volumetric and surface SFLs in terms of the molecular gas do not show any noticeable difference. The volumetric SFL for the total gas has a flatter power-law slope of 1.26 with a smaller scatter of 0.19 dex compared to the slope (2.05) and the scatter (0.25 dex) of the surface SFL. The molecular gas SFLs have similar slopes of 0.78 (volume density) and 0.77 (surface density) with the same rms scatter. We show that the interstellar gas pressure is strongly correlated with the SFR but find no significant difference between the correlations based on the volume and surface densities.
In order to quantify the relationship between gas accretion and star formation, we analyse a sample of 29 nearby galaxies from the WHISP survey which contains galaxies with and without evidence for ...recent gas accretion. We compare combined radial profiles of FUV (GALEX) and IR 24 {\mu}m (Spitzer) characterizing distributions of recent star formation with radial profiles of CO (IRAM, BIMA, or CARMA) and HI (WSRT) tracing molecular and atomic gas contents to examine star formation efficiencies in symmetric (quiescent), asymmetric (accreting), and interacting (tidally disturbed) galaxies. In addition, we investigate the relationship between star formation rate and HI in the outer discs for the three groups of galaxies. We confirm the general relationship between gas surface density and star formation surface density, but do not find a significant difference between the three groups of galaxies.
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