Star formation in normal galaxies

The ways in which recent infrared observations, particularly by the Infrared Astronomy Satellite (IRAS), have influenced ideas about star formation in normal galaxies, are discussed

Ground-based 1- to 32-microns observations of ARP 220: Evidence for a dust-embedded AGN?

New observations of the 10 and 20 micron size of the emission region in Arp 220 are presented. Also given are ground based photometry from 1 to 32 micron including measurements of the strength of the silicate feature at 10 micron. The results show that the 20 micron size of Arp is smaller than 1.5 arcsec (500 pc); comparison of IRAS and ground based observations show that IRAS 12 micron flux measured with a large arcmin beam is the same as that seen from the ground with a 3 arcsec aperture. At 10 micron a deep silicate absorption feature is seen that corresponds to a visual extinction of about 50 mag. These results suggest that a very significant portion of the 10 to the 12th power L sub 0 infrared luminosity from Arp 220 comes from a region less than or of the order of 500 pc in diameter. When these results are combined with recent measurement of a broad Brackett alpha line by DePoy and an unresolved 2.2 micron source by Neugebauer, Matthews and Scoville, a very attractive possibility for the primary luminosity source Arp 220 is a dust embedded compact Seyfert type nucleus

VLA observations of a sample of galaxies with high far-infrared luminosities

Preliminary results are presented from a radio survey of galaxies detected by the IRAS minisurvey. It was found that the main difference between galaxies selected in the far infrared and those selected in the optical is that the former have higher radio luminosities and that the radio emission is more centrally concentrated. There is some evidence that the strong central radio sources in the galaxies selected in the infrared are due to star formation, the star formation rate divided by the volume in which the star formation is occuring is 100 to 1000 times greater in the galaxies selected in the infrared than in the disks of normal galaxies

Ultraviolet protection on a snowball Earth

Habitats in the Antarctic provide an insight into habitats available on snowball earth. Physical UV protection on snowball earth would have been dominated by the manifestations of ice and snow in different habitats. The snowball period was a golden age of UV protection

Two-micron spectrophotometry of the galaxy NGC 253

A very strong Brackett-gamma hydrogen emission line, and the 2.3 micron CO stellar absorption feature were measured in NGC 253. The presence and strength of the CO feature indicates that late type giant stars produce most of the 2.2 micron continuum emission, while the rate of ionization implied by strength of the Brackett-gamma line indicates that much, perhaps all, of the luminosity detected at far infrared wavelengths originates from a large number of OB stars. As compared to the corresponding region of the Galaxy, the number of massive young stars in the central 200 pc of NGC 253 is thirty times greater, but the total mass of stars is roughly the same

8-13 micron spectroscopy of NGC 253: a spatially resolved starburst

NGC 253 is a nearby spiral galaxy that is currently undergoing a nuclear burst of star formation in a 100 pc diameter region. We present spatially resolved 8--13 micron low-resolution spectra at four positions along the ridge of 8--13 micron emission. We find that the relative strengths of the ionic, dust emission features, and dust continuum emission vary with position in the galaxy but can be accounted for everywhere without recourse to extinction by silicates. The brightest mid-infrared peak (which is displaced from the nucleus) has elevated levels of both continuum and 11.1--12.9 micron `plateau' emission, indicative of dust heated within a photo-dissociation region. Spectra obtained over the course of 3 yr at the position of the brightest mid-infrared peak show no significant time variation.Comment: 8 pages, 3 figures, to appear in MNRA

Infra-Red Sources in the H II Region W₃

High resolution mapping and photometric observations in the wavelength range 1.65–20 µ have led to the discovery of nine distinct infra-red objects in W₃. Four of them, including one coincident with W₃ (OH), are identified with compact radio H II condensations ∼0.1 pc in diameter. They show strong emission in the range 3–20 µ which is attributable to dust grains at a temperature of ∼ 150 K mixed with the ionized gas. On the other hand, the 2-µ emission from these objects is considerably less than is predicted from the radio measurements, indicating that the H II condensations are surrounded by obscuring dust with up to 50 mag of visual extinction. One of the condensations contains an unresolved source which is almost certainly a highly obscured O star that excites the component. Four other infra-red sources have no associated radio continuum source; one of these, an unresolved source with a luminosity ∼3 × 10⁴ L⊙ is coincident with a source of H₂O maser emission and may be a massive protostar

Infra-Red Sources in the H II Region W₃

High resolution mapping and photometric observations in the wavelength range 1.65–20 µ have led to the discovery of nine distinct infra-red objects in W₃. Four of them, including one coincident with W₃ (OH), are identified with compact radio H II condensations ∼0.1 pc in diameter. They show strong emission in the range 3–20 µ which is attributable to dust grains at a temperature of ∼ 150 K mixed with the ionized gas. On the other hand, the 2-µ emission from these objects is considerably less than is predicted from the radio measurements, indicating that the H II condensations are surrounded by obscuring dust with up to 50 mag of visual extinction. One of the condensations contains an unresolved source which is almost certainly a highly obscured O star that excites the component. Four other infra-red sources have no associated radio continuum source; one of these, an unresolved source with a luminosity ∼3 × 10⁴ L⊙ is coincident with a source of H₂O maser emission and may be a massive protostar

Two-micron line emission from the H II region G 333.6 – 0.2

Spectrophotometry of the H II region G333.6 – 0.2 with λ/Δλ≏100 shows strong emission lines of hydrogen and helium super-imposed on a continuum. Spatial variations in the equivalent widths of the lines suggest the presence of very hot (⁠⩾600K⁠) dust grains within the region. The shape of this very powerful H II region indicates that its dense ionized core is being continuously replenished from a reservoir of neutral gas