Large Galactocentric Radii Research Articles

Faint Photometry of Edge-on Spiral Galaxies: A Search for Massive Halos

Upper limits have been set to the luminosity from the massive halos of three late-type edge-on spiral galaxies: NGC 2683 (Sb), NGC 4244 (Scd), and NGC 5907 (Sc). The limits resulted from simultaneous photometry in the visual (V) and 2.2μm (K) photometric bands which is sensitive to both luminosity and color changes along the minor axes of the three galaxies. The 3σ lower limits to the mass-to-light ratios for the halo of NGC 5907 are the largest ever recorded: M/Lv > 2000 and M/Lk > 64 in solar units. Since K band M/L for M-dwarf stars lying just above the hydrogen-burning limit is about 35, the results virtually eliminate the possibility that hydrogen-burning stars comprise more than a fraction of the halo masses. If the halos contain a more realistic spectrum of stellar masses, for example Population II, the visual band measurements imply that these stars account for less than one percent of the halo mass. Similar limits were obtained for NGC 4244 and NGC 2683. Variations of the V-K colors along and perpendicular to the disks show no sign of population changes toward redder objects at large galactocentric radii.

Faint photometry of edge-on spiral galaxies - A search for massive halos

view Abstract Citations (37) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Faint photometry of edge-on spiral galaxies : a search for massive halos. Skrutskie, M. F. ; Shure, M. A. ; Beckwith, S. Abstract Upper limits have been set to the luminosity from the massive halos of three late-type edge-on spiral galaxies: NGC 2683 (Sb), NGC 4244 (Scd), and NGC 5907 (Sc). The limits resulted from simultaneous photometry in the visual (V) and 2.2-micron (K) photometric bands which is sensitive to both luminosity and color changes along the minor axes of the three galaxies. The mass-to-light ratios for the halo of NGC 5907 are the largest ever recorded: M/L(V) greater than 2000 and M/L(K) greater than 64 in solar units. The results virtually eliminate the possibility that hydrogen-burning stars comprise more than a fraction of the halo masses. Variations of the V-K color along and perpendicular to the disks show no sign of population changes toward redder objects at large galactocentric radii. The nucleus of NGC 5907 contains an unresolved source less than 330 pc in size with a 2.2-micron luminosity of order 5 x 10 to the 9th solar luminosity and may be an example of a starburst galactic nucleus overlooked by visual observations. Publication: The Astrophysical Journal Pub Date: December 1985 DOI: 10.1086/163701 Bibcode: 1985ApJ...299..303S Keywords: Astronomical Photometry; Galactic Radiation; Halos; Spiral Galaxies; Colorimetry; Galactic Nuclei; Luminous Intensity; Mass To Light Ratios; Metallicity; Point Sources; Starburst Galaxies; Astrophysics full text sources ADS | data products SIMBAD (3) NED (3)

Atomic and Molecular Gas in the Inner Regions of the Milky Way and Other Galaxies

It seems likely that we inhabit a galactic system which in its gross characteristics exemplifies the present meaning of the word “normal”. The general framework for interpreting the distribution and kinematics of the observed gas consists of a well-defined rotation curve, applicable over the great majority of a thin, nearly flat disk; the stars and gas within this disk are generally quite cold, having little energy in random as opposed to well-ordered motions. In fact, neutral gas in the galactic disk is sufficiently regular in its structure that no grand pattern of spiral arms stands out in sharp relief.As one moves inward in the Galaxy from the location of the Sun, this regularity persists to within about 4 kpc of the center, at which distance the abundance of gas in either atomic or molecular form drops fairly abruptly. Inside this region, the character of the gas distribution undergoes a marked change and the behaviour observed there, while it may be common to even the best-ordered systems, represents a rather spectacular departure from the organization at larger galacto-centric radii. As the gas abundance increases once more toward the galactic center it is seen to reside in a multitude of individual features having disparate spatial and kinematic properties. Many of these have large and/or obvious components of non-circular motion, usually taken as indicating expulsion of matter from the galactic center region at both large and small angles with respect to the rotation axis of the galaxy at large. Others, while occurring at velocities whose sign is consistent with rotation motion alone, have contradictory changes in velocity with position. Line profiles taken in the inner regions of the Galaxy are generally decomposed according to catalogs of classifiable features but no generally accepted interpretative framework exists as a means of relating the wide variety of observable phenomena.

UBV photometry of the anticenter cluster Berkeley 21

UBV photometry of approximately 200 stars in the faint anticenter cluster, Berkeley 21, was obtained primarily with the Kron electronic camera. Analysis of the color--magnitude and two-color diagrams indicates that Be21 is a highly reddened (E (B-V) approx.1.0) cluster resembling clusters found in the Magellanic Clouds. Since the Magellanic Clouds are known to be metal poor with respect to the Galaxy, the results suggest that objects located at large galactocentric radii may be quite metal deficient, in agreement with recent theoretical models of the chemical evolution of the Galaxy. The cluster exhibits an ultraviolet excess of about 0.3 mag, which supports the idea that the cluster is metal poor. Estimates of the distance modulus place the object 10--15 kpc from the sun, that is, 20--25 kpc from the galactic center.