Engineering topics

Brinks, Elias

Publications and source records attributed to Brinks, Elias.

7 records

DOE OSTI2021

Herschel Photometric Observations of Little Things Dwarf Galaxies

We present here far-infrared photometry of galaxies in a sample that is relatively unexplored at these wavelengths: low-metallicity dwarf galaxies with moderate star formation rates. Four dwarf irregular galaxies from the Little Things survey are considered, with deep Herschel PACS and SPIRE observations at 100, 160, 250, 350, and 500 μm. Results from modified blackbody fits indicate that these galaxies have low dust masses and cooler dust temperatures than more actively star-forming dwarfs, occupying the lowest L {sub TIR} and M {sub dust} regimes seen among these samples. Dust-to-gas mass ratios of ∼10{sup −5} are lower, overall, than in more massive and active galaxies but are roughly consistent with the broken power-law relation between the dust-to-gas ratio and metallicity found for other low-metallicity systems. Chemical evolution modeling suggests that these dwarf galaxies are likely forming very little dust via stars or grain growth and have very high dust destruction rates.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Outflow from Outer-arm Starburst in a Grazing Collision between Galaxies

Gemini NIFS K-band spectra and Atacama Large Millimeter/submillimeter Array {sup 12}CO J=1→0, HCO{sup +}, and 100 GHz continuum observations are used to study a bright starburst clump on an outer arm of the interacting galaxy NGC 2207. This clump emits 23% of the total 24 μm flux of the galaxy pair and has an optically opaque dust cone extending out of its 170 pc core. The measured CO accounts for the dark cone extinction if almost all the gas and dust there are in front of the star clusters. An associated approaching CO outflow has v {sub z} ~ 16 km s{sup -1}, an estimated molecular mass 8 × 10{sup 6} M {sub ⊙}, and rises to heights ~0.9 kpc. A receding CO outflow on the far side with v {sub z} ~ 28 km s{sup -1} is less extensive. The observed star formation in the core over 10 Myr can supply the dark cone kinetic energy of roughly 2 × 10{sup 52} erg via supernovae and stellar winds. Other signs of intense activity are a variable radio continuum, suggesting an embedded supernova or other outburst; X-ray emission possibly from an X-ray binary or intermediate-mass black hole, depending on the extinction; and Brγ and He i lines with 82 km s{sup -1} line widths and fluxes consistent with excitation by embedded O-type stars. According to previous models, the retrograde encounter suffered by NGC 2207 caused the loss of angular momentum. This compressed its outer disk. We suggest that the resulting inward crashing stream hit a massive H i clump on the preexisting spiral arm and triggered the observed starburst.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1994

Star formation thresholds in H II galaxies with H I companions

We present high resolution Very Large Array (VLA) 21 cm line observations of five H II galaxies combined with previous lower resolution data from Taylor et al. (1993) and optical broadband R and H-alpha Charge Coupled Device (CCD) images of the systems. Following Kennicutt (1989) we calculated the threshold H I surface density for star formation for the H II galaxies and compared the location and shape of this predicted threshold density contour with the optical shape of the galaxies. We find generally a good correlation between these two, although a constant density contour of 10(exp 21)/sq cm fits the images of the optical galaxies equally as well. The H I synthesis observations have revealed that the H II galaxies have sharply peaked H I radial profiles, in contrast to the relatively flattened profiles of low surface brightness (LSB) galaxies, suggesting that large central concentrations of gas are a necessary condition for the occurrence of bursts of massive star formation seen in H II galaxies. These observations are consistent with the hypothesis that LSB galaxies represent the quiescent phase of H II galaxies, if a suitable mechanism exists (such as galaxy interactions) to cause H I to concentrate at the center of LSB galaxies prior to the onset of the burst of star formation. However, it is noted that the H II galaxies (and dwarf galaxies in general) span a relatively large range in mass. Since many properties correlate with mass (e.g., gas mass fraction), we point out that great care needs to be taken in choosing the proper comparison samples of LSB and H II galaxies.

Taylor, Christopher L.↗

NASA NTRS1993

High velocity clouds in nearby disk galaxies

Clouds of neutral hydrogen in our galaxy with the absolute value of v greater than 100 km/s cover approximately 10 percent of the sky to a limiting column density of 1 x 10(exp 18) cm(exp -2). These high velocity clouds (HVCs) may dominate the kinetic energy of neutral hydrogen in non-circular motion, and are an important though poorly understood component of galactic gas. It has been suggested that the HVCs can be reproduced by a combination of three phenomena: a galactic fountain driven by disk supernovae which would account for most of the HVCs, material tidally torn from the Magellanic Clouds, and an outer arm complex which is associated with the large scale structure of the warped galactic disk. We sought to detect HVCs in external galaxies in order to test the galactic fountain model.

Schulman, Eric↗

NASA NTRS1993

The critical density for star formation in HII galaxies

The star formation rate (SFR) in galaxies is believed to obey a power law relation with local gas density, first proposed by Schmidt (1959). Kennicutt (1989) has shown that there is a threshold density above which star formation occurs, and for densities at or near the threshold density, the DFR is highly non-linear, leading to bursts of star formation. Skillman (1987) empirically determined this threshold for dwarf galaxies to be approximately 1 x 10(exp 21) cm(exp -2), at a linear resolution of 500pc. During the course of our survey for HI companion clouds to HII galaxies, we obtained high resolution HI observations of five nearby HII galaxies. HII galaxies are low surface brightness, rich in HI, and contain one or a few high surface brightness knots whose optical spectra resemble those of HII regions. These knots are currently experiencing a burst of star formation. After Kennicutt (1989) we determine the critical density for star formation in the galaxies, and compare the predictions with radio and optical data.

Taylor, Christopher L.↗

NASA NTRS1990

The violent interstellar medium in Messier 31

Taurus observations in the line of H alpha and Very Large Array (VLA) HI mapping of the HII complex No. 722 in M31, reveal what seems to be a spherical cavity 330 pc in diameter blown out by a stellar association of over 20(exp 6) years old. Evidence of induced star formation which was initiated less than 5(exp 6) years ago is present in the form of bright HII emission and numerous O, B and Wolf-Rayet stars which are found within the shell surrounding the cavity. The energy necessary to create the HI shell is estimated to be about 5(exp 51) erg.

Brinks, Elias↗

NASA NTRS1988

An H I absorption line survey of Messier 31

The 21-cm absorption through the disk of M31 has been observed, using the VLA to study the cool atomic phase of the interstellar medium in this nearby spiral galaxy. It is found that the abundance of diffuse clouds with tau between 0.125 and 1 in M31 is no higher than in the solar neighborhood of the Milky Way. The mean spin temperature, 300 K, is similar to or higher than the local value. The fraction of the neutral atomic hydrogen in the cool phase is about 0.25 or less. These results imply that M31 has a mixture of warm and cool interstellar phases similar to that in our vicinity of the Milky Way, which suggests either that the heating and cooling balance occurs in a similar pressure environment, or that whatever dynamical processes determine the mixture of warm and cool gas reach a similar equilibrium in M31 as here. Specifically, the warm neutral medium seems to be a robust phase, with a much larger filling-factor than the cool clouds.

Dickey, John M.↗