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At least 235 records · Page 13
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NASA NTRS1983

Luminosity distributions for Virgo cluster galaxies. I Near-infrared surface photometry of 81 disk systems

I-band (8500 A) surface photometry of 81 galaxies in Virgo provides the basis for comparing the disk properties of S0 galaxies with those of Sa, Sb, and Sc systems. No significant difference is found in the distributions of either central surface brightness or exponential scale length between S0's and later Hubble types. Because the I-band is dominated by contributions from the old-disk population, this result suggests that the factors which control the distribution of luminous disk material in all types of disk systems are identical. Evidently, environmental factors have not played a significant role in affecting the star-forming histories of the Virgo disks.

Boroson, T. A.↗
NASA NTRS1993

Infrared Cirrus and Discrete Sources in the Outer Galaxy

Studies of Galactic infrared cirrus have been based on observations of individual high latitude clouds, analysis of large scale emission at high latitudes in the Solar Neighborhood and complete linear decomposition of the global emission from IRAS and other observations over the entire Galaxy.

IRAS infrared cirrus linear decomposition Point So↗
NASA NTRS1987

Stellar bars and the spatial distribution of infrared luminosity

Ground-based 10 micron observations of the central region of over 100 infrared luminous galaxies are presented. A first order estimate of the spatial distribution of infrared emission in galaxies is obtained through a combination of ground-based and Infrared Astronomy Satellite (IRAS) data. The galaxies are nearby and primarily noninteracting, permitting an unbiased investigation of correlations with Hubble type. Approximately 40% of the early-type barred galaxies in this sample are associated with enhanced luminosity in the central (approximately 1 kpc diameter) region. The underlying luminosity source is attributed to both Seyfert and star formation activity. Late-type spirals are different in that the spatial distribution of infrared emission and the infrared luminoisty are not strongly dependent on barred morphology.

Devereux, Nicholas↗
NASA NTRS2020

A Catalog of Emission-line Galaxies from the Faint Infrared Grism Survey: Studying Environmental Influence on Star Formation

We present a catalog of 208 0.3 < z < 2.1 emission-line galaxies (ELGs) selected from 1D slitless spectroscopy obtained using Hubble's WFC3 G102 grism, as part of the Faint Infrared Grism Survey. We identify ELG candidates by searching for significant peaks in all continuum-subtracted G102 spectra and, where possible, confirm candidates by identifying consistent emission lines in other available spectra or with published spectroscopic redshifts. We provide derived emission-line fluxes and errors, redshifts, and equivalent widths for Hα λ6563, [O iii] λλ4959, 5007, and [O ii] λ3727 emission lines, for ELGs down to AB(F105W) >28 and >10^(−17) erg/ sq. cms line flux. We use the resulting line catalog to investigate a possible relationship between line emission and a galaxy's environment. We use seventh-nearest-neighbor distances to investigate the typical surroundings of ELGs compared to non-ELGs, and we find that [O iii] emitters are preferentially found at intermediate galaxy densities near galaxy groups. We characterize these ELGs in terms of the galaxy specific star formation rate (SFR) versus stellar mass and find no significant influence of environment on that relation. We calculate SFRs and find no dependence of SFR on local galaxy surface density for 0.3 < z < 0.8 Hα emitters and for 0.8 < z < 1.3 [O iii] emitters. We find similar rates of close-pair interaction between ELGs and non-ELGs. For galaxy surface densities Σ ≤ 30 Mp/sq.c, we find no consistent effect of environment on star formation.

John Pharo↗
NASA NTRS1985

Star formation in the inner Galaxy - A far-infrared and radio study of two H II regions

Far-infrared and radio continuum maps have been made of two inner-Galaxy H II region complexes, G30.8-0.0 and G25.4-0.2, along with radio and molecular line measurements at selected positions. The far-IR emission from each region is dominated by two sources. For both G25.4 and G30.8, the distribution of the emission is similar to that of the radio emission, indicating that OB stars provide most of the heating. There is evidence that extinction plays an important role in G30.8, even in the far-IR. A near-IR point source has been detected in G30.8 at the position of peak far-IR color temperature. This source may be the ionizing star for the core of G30.8. Measurement of forbidden S III 9532 A from G25.4SE indicates that the extinction toward this source is very low, which is difficult to reconcile with previously determined distance measurements to this source.

Lester, D. F.↗
NASA NTRS1995

An infrared imaging study of galaxies in the local universe

This poster was a preliminary report on a survey of galaxies in the local universe at J and K using a NICMOS3 256 x 256 infrared photometric camera attached to the 61 inch telescope on Mt. Bigelow. Deep images are being obtained for a representative sample of galaxies in the Uppsala General Catalogue. Structural and color parameters are determined for a wide variety of galactic types. These data should prove to be valuable in characterizing stellar populations within disks and bulges, determining if IR-active galaxies have unusual global as well as- nuclear properties, and understanding the effects of evolution and redshift dimming in distant galaxies.

Grauer, Albert D.↗
NASA NTRS1990

Starbursts in interacting galaxies: Observations and models

Starbursts have been a puzzling field of research for more than a decade. It is evident that they played a significant role in the evolution of many galaxies but still quite little is known about the starburst mechanisms. A way towards a better interpretation of the available data is the comparison with evolution models of starburst. The modelling of starbursts and the fitting of such model starbursts to observed data is discussed. The models were applied to a subset of starburst and post-starburst galaxies in a sample of 30 interacting systems. These galaxies are not ultraluminous far infrared (FIR) galaxies but rather ordinary starburst galaxies with FIR luminosities of a few 10(exp 10) to a few 10(exp 11) solar luminosities.

Bernloehr, Konrad↗
NASA NTRS1991

The relation between infrared and radio emission in spiral galaxies

A remarkable correlation between the far infrared and the radio continuum emission of star forming galaxies was one of the early results based on IRAS data, and has remained one of the most intriguing. Recent work has extended the correlation to early type galaxies, revealing a slightly different ratio in lenticulars. When radio and infrared maps of disk galaxies are compared, the radio disks appear systematically more diffuse. This has been interpreted as a manifestation of the diffusion of cosmic-ray electrons, and has allowed a fresh look at the behavior of magnetic fields and cosmic rays in spiral galaxies, and at their relation to the rest of the interstellar medium.

Helou, George↗
NASA NTRS2004

Near-infrared colors of submillimeter-selected galaxies

We report on deep near-infrared (NIR)observations of submillimeter-selected galaxies (SMGs) with the Near-Infrared Camera (NIRC) on the Keck I telescope. We have identified K-band candidate counterparts for 12 out of 15 sources in the SCUBA Cluster Lens Survey. Three SMGs remain nondetections with K-band limits of K > 23 mag, corrected for lensing. Compensating for lensing, we find a median magnitudeof K = 22 ± 1 mag for the SMG population, but the range of NIR flux densities spans more than a factor of 400.

galaxies↗
NASA NTRS1985

Star formation in the inner galaxy: A far-infrared and radio study of two H2 regions

Far-infrared and radio continuum maps have been made of the central 6' of the inner-galaxy H II regions G30.8-0.0 (in the W43 complex) and G25.4-02., along with radio and molecular line measurements at selected positions. An effort is made to understand far infrared wavelingths allow the dust temperature structures and total far infrared fluxes to be determined. Comparison of the radio and infrared maps shows a close relationship between the ionized gas and the infrared-emitting material. There is evidence that parts of G30.8 are substantially affected by extinction, even at far-infrared wavelengths. For G25.4-0.2, the radio recombination line and CO line data permit resolution of the distance ambiguity for this source. The confusion in distance determination is found to result from an extraordinary near-superposition of two bright H II regions. Using revised distances of 4.3 kpc for G26.4SE and 12 kpc for G25.4NW, that the latter, which is apparently the fainter of the two sources, is actually the more luminous. Though it is not seen on the Palomar Sky Survey, G25.4SE is easily visible in the 9532A line of S III and is mapped in this line. The ratio of total luminosity to ionizing luminosity is very similar to that of H II regions in the solar circle. Assuming a coeval population of ionizing stars, a normal initial mass function is indicated.

Lester, D. F.↗
NASA NTRS1985

Star formation in the inner galaxy: A far-infrared and radio study of two H2 regions

Far-infrared and radio continuum maps have been made of the central 6' of the inner-galaxy HII regions G30.8-0.0 (in the W43 complex) and G25.4-0.2, along with radio and molecular line measurements at selected positions. The purpose of this study is an effort to understand star formation in the molecular ring at 5 kpc in galactic radius. Measurements at several far infrared wavelengths allow the dust temperature structures and total far infrared fluxes to be determined. Comparison of the radio and infrared maps shows a close relationship between the ionized gas and the infrared-emitting material. There is evidence that parts of G30.8 are substantially affected by extinction, even at far-infrared wavelengths. Using radio recombination line and CO line data for G25.4-0.2, the distance ambiguity for this source is resolved. The large distance previously ascribed to the entire complex is found to apply to only one of the two main components. The confusion in distance determination is found to result from an extraordinary near-superposition of two bright HII regions. Using the revised distances of 4.3 kpc for G25.4SE and 12 kpc for G25.4NW, it is found that the latter, which is apparently the fainter of the two sources, is actually the more luminous. The ratio of total luminosity to ionizing luminosity is very similar to that of HII regions in the solar circle. Assuming a coeval population of ionizing stars, a normal initial mass function is indicated.

Lester, D. F.↗
NASA NTRS1991

High resolution infrared astronomy satellite observations of a selected spiral galaxy

The H I, infrared, CO, H alpha and H beta band observations of M51, the prototypical grand-design spiral galaxy, are used to study the consequences of star formation for the distribution of H I and dust. Using the new Very Large Array (VLA) map of 21 cm emission, the Owens Valley Radio Observatory CO mosaic map, and an H alpha imate, new tests were performed with the idea of Tilanus and Allen that the H I is largely a photodissociation product in star-forming regions. It is confirmed that the H I spiral arms are generally coincident with the H II region arms, and offset downstream from the CO arms. The radial distributions of total gas, H alpha and H I surface density have a simple explanation in the dissociation picture. The distributions also demonstrate how the surface density of H I might be related to the star formation efficiency in molecule-rich galaxies. The large width of the H I regions along the arms compared to that of the giant H II regions can be understood in terms of a simple calculation of the expected size of an H I region associated with a typical giant H II region. The longer lifetime of the stars producing dissociating radiation vs. those producing ionizing radiation and the relatively long molecular formation timescale will also contribute to the greater width of the H I arms if stars are continuously forming on the arms. The lack of detailed coincidence of the H I and H II regions along the inner arms has a variety of possible explanations. Two simple tests were performed to probe the origins of the IRAS emission in M51. First, it was found that the infrared excess (IFE) of M51 is 24, suggesting that a substantial fraction of the infrared emission arises from dust heated by photons which do not originate in massive star-formaing regions. Second, radial cuts through the IRAS bands show that at 12, 25, and 60 microns, the arm-interarm contrast of the IRAS emission is substantially less than that of the H alpha emission, providing further evidence for the explanation and for the existence of a broadly distributed dust component. Deconvolved IRAS maps have improved resolution but do not change this finding.

Kulkarni, S. R.↗
NASA NTRS1988

The link between IRAS spectra and near-infrared emission features in external galaxies

The relationship in external galaxies between the presence of the near-infrared (NIR) emission features attributed to polycyclic aromatic hydrocarbon (PAH) molecules, and the far-infrared (FIR) properties as observed by IRAS, is investigated. It is found that whenever the NIR features are absent in a galaxy, the FIR spectrum displays an enhancement at shorter wavelengths relative to normal galaxies. This enhancement is always associated with a strong activity in the galactic nucleus. Some Seyfert galaxies do not exhibit such an infrared signature and therefore they are probably energetically dominated by star-formation processes. Finally, the importance of hard UV photons and of the hot medium in the narrow line region of active nuclei is emphasized in relation to the survival of the PAH molecules. In this frame, the absence of PAHs in the galactic center could be taken as evidence for the presence of an active nucleus.

Desert, F. X.↗
NASA NTRS1987

Infrared spectroscopy of star formation in galaxies

The Brackett alpha and beta lines with 7.2 seconds angular and 350 km/s velocity resolution were observed in 11 infrared-bright galaxies. From these measurements extinctions, Lyman continuum fluxes, and luminosities due to OB stars were derived. The galaxies observed to date are NGC3690, M38, NGC 5195, Arp 220, NGC 520, NGC660, NGC1614, NGC 3079, NGC 6946, NGC 7714, and Maffei 2, all of which were suggested at some time to be starburst ogjects. The contributions of OB stars to the luminosities of these galaxies can be quantified from the measurements and range from insignificant to sufficient to account for the total energy output. The OB stellar luminosities observed are as high as 10 to the 12th solar luminosities in the galaxy NGC 1614. It is noteworthy that star formation can play very different roles in the infrared energy output of galaxies of similar luminosity, as for example Arp 220 and NGC 1614. In addition to probing the star formation process in these galaxies, the Brackett line measurements, when compared to radio and infrared continuum results, have revealed some unexpected and at present imperfectly understood phenomena: in some very luminous sources the radio continuum appears to be suppressed relative to the infrared recombination lines; in many galaxies there is a substantial excess of 10 micron flux over that predicted from simple models of Lyman alpha heating of dust if young stars are the only significant energy source.

Beck, Sara C.↗
NASA NTRS2013

Dusty Feedback from Massive Black Holes in Two Elliptical Galaxies

Far-infrared dust emission from elliptical galaxies informs us about galaxy mergers, feedback energy outbursts from supermassive black holes and the age of galactic stars. We report on the role of AGN feedback observationally by looking for its signatures in elliptical galaxies at recent epochs in the nearby universe. We present Herschel observations of two elliptical galaxies with strong and spatially extended FIR emission from colder grains 5-10 kpc distant from the galaxy cores. Extended excess cold dust emission is interpreted as evidence of recent feedback-generated AGN energy outbursts in these galaxies, visible only in the FIR, from buoyant gaseous outflows from the galaxy cores.

Galaxies↗
NASA NTRS1997

A Near-Infrared Imaging Study of Seyfert Galaxies with Extended Emission line Regions

We present a near-infrared J,H,K and L' band (1.25 - 3.80 mue) imaging study of a sample of Seyfert galaxies, including some of the best studied examples of these with extended emission line regions (EELR). The observed near-IR nuclear colors are consistent with mixture of emmisions from an old stellar population and unredening hot dust.

Near-Infrared Seyfert Galaxies↗
NASA NTRS1985

Near-infrared mapping of ARP 299 (IC 694-NGC 3690) - Colliding galaxies unveiled

Near-infrared maps and multicolor photometry of the interacting galaxies IC 694 and NGC 3690 which form Arp 299 (= Markarian 171) are presented. These data reveal for the first time the distribution of nuclei and old red stars in a cataclysmically interacting system. The nuclei are considerably offset from the visual centroids of the galaxies but not from the mass centroids. The near-infrared colors of the most active regions are strongly affected by extinction, emission form hot dust, and bremsstrahlung. Near-infrared emission is also identified with secondary regions of star formation, probably resulting from the galaxies' interaction.

Telesco, C. M.↗
NASA NTRS1982

Far-infrared observations of Sagittarius A - The luminosity and dust density in the central parsec of the Galaxy

Far-infrared observations of the central 4 arcmin of the Galaxy with 30-arcsec resolution made simultaneously at 30 microns, 50 microns, and 100 microns are presented. The 30-micron radiation peaks strongly at the position of the galactic center, as determined from the 2-micron surface brightness and the density of ionized gas. The 50- and 100-micron emission is much more extended along the plane and shows two emission lobes, one on either side of the 30-micron peak. At the position of the galactic center itself there is a local minimum in the 100-micron surface brightness. It is concluded that the dust density decreases inward over the central few parsecs of the Galaxy and that the dust density in the central parsec is so low that optical and ultraviolet radiation freely traverses this region. The total luminosity of the sources heating the dust which radiates the far-infrared emission from the central few parsecs is deduced to be between 1 x 10 to the 7th and 3 x 10 to the 7th solar luminosities.

Becklin, E. E.↗