Nearby Sculptor Group Research Articles

Angular Momentum in the Sculptor Group

The spins of the major galaxies in the nearby Sculptor Group agree with those calculated to be produced by tidal interactions among themselves. The agreement is closer than would be expected from published uncertainties in distances, indicating either that these uncertainties are smaller than calculated or that they are correlated. Three pairs of galaxies (NGC 55 and 300, 247 and 253, and 45 and 7793) are in approximate two-body orbits; the direction of orbital angular momentum for the first two pairs is derived.

The Stellar Content of Local Group Galaxies: IAU Symposium 19211Conference was held in Cape Town, South Africa, in 1998 September. Proceedings will be edited by P. A. Whitelock and R. D. Cannon and published in the ASP Conference Series.

IAU Symposium 192 was both broader and narrower than its title would suggest. As will be discussed below, this meeting covered many aspects of the Local Group other than stellar content. On the other hand, discussion of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) was cut back, since a previous IAU Symposium (190) on the Magellanic Clouds had been held only 2 months earlier in Victoria, Canada. Local Group membership.—A substantial portion of the conference was devoted to the fundamental question of Local Group (LG) membership, with review papers by both E. K. Grebel and T. E. Armandroff touching on this subject. In the last year the number of known companions to M31 has doubled, thanks to work by Armandroff, I. D. Karachentsev, and collaborators. The Armandroff search is based on a matched filter applied to the Digital Sky Survey and has produced many more candidates that are still being investigated. However, all the new LG objects to date are brighter than , M 10 v suggesting that many other fainter galaxies are lurking, waiting to be discovered. (Contrast this work on M31 companions with a search by M. Irwin and collaborators, who have turned up only one new object after searching two-thirds of the sky.) On several occasions it was remarked that NGC 55 (which is usually considered to be a member of the nearby Sculptor Group) lies on the zero velocity surface of the Local Group and may actually be considered a member of our Group. (A recent preprint by H. Jerjen et al. [astro-ph/9809046] suggests that it may be more appropriate to consider the Local and Sculptor Groups as a single supergalactic structure.) A related question is that of the luminosity function of the Local Group. If the inventory of LG galaxies is not complete below 10, then one cannot rule out the possibility of a steep upturn in the LG luminosity function (as observed in some other samples of galaxy populations). Morphology.—Sidney Van den Bergh highlighted the absence of large dwarf spheroidals (such as those in the Virgo cluster or the one known in the M81 Group). K. Freeman pointed out the difference in the structure of bulges in earlytype systems (e.g., M31, the Sombrero galaxy, etc.) that possess

The Spectacular Ionized Interstellar Medium of NGC 55

We present deep Halpha+[NII], [SII] (6716,6731A) and [OII] (3726,3729A) images of the highly inclined, actively star--forming SBm galaxy NGC 55, located in the nearby Sculptor Group. Due to its proximity, NGC 55 provides a unique opportunity to study the disk--halo interface in a late--type galaxy with unprecedented spatial resolution. Our images reveal a spectacular variety of ionized gas features, ranging from giant HII region complexes, to supergiant filamentary and shell features, to patches of very faint diffuse emission. Many of these features protrude well above the plane of the galaxy, including a very faint fragmented shell of emission which is visible at 2.6 kpc above the disk. We identify candidate `chimneys' extending out of the disk, which could be the conduits into the halo for hot gas around disk star-forming regions, and could also provide low-density paths for the passage of UV photons from the disk to the halo. Several of the identified chimneys are `capped' with clumps of ionized gas, one of which, located at 1.5 kpc above the disk plane, appears to be the site of recent star formation. Emission--line ratios ([OII]/Halpha+[NII], [SII]/Halpha+[NII]) constrain the ionization mechanism of the gas, and our images allow the first measurement of [OII]/Halpha+[NII] in extra-planar diffuse ionized gas. The diffuse gas is characterized by emission--line ratios which are enhanced on average by a factor of two compared to those of bright HII regions. Each line ratio increases in value smoothly from the cores of HII regions, through the haloes of HII regions, into the diffuse ionized gas. Such a continuous trend is predicted by models in which the diffuse gas is ionized by photons produced by massive stars in HII regions.

Diffuse Ionized Gas in Spiral Galaxies: Probing Lyman Continuum Photon Leakage From H II Regions?

view Abstract Citations (176) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Diffuse Ionized Gas in Spiral Galaxies: Probing Lyman Continuum Photon Leakage From H II Regions? Ferguson, Annette M. N. ; Wyse, Rosemary F. G. ; Gallagher, J. S., III ; Hunter, Deidre A. Abstract As part of a large study to map the distribution of star formation across galactic disks, we have obtained deep Hα images of the nearby Sculptor Group spirals NGC 247 and NGC 7793. These images are of sufficiently high quality that they allow identification and analysis of diffuse Hα emission at surface brightness levels ranging from those of extremely low density H II regions down to those of the local Galactic disk diffuse emission. This paper presents a study of the large scale distribution and global energetics of diffuse ionized gas (DIG) in these galaxies and investigates the association between DIG and discrete H II regions. The radial and azimuthal intensity distributions of the DIG reveal that it is highly correlated with bright H II regions over both small and large scales. The observed Hα luminosities of the DIG are considerable and account for 30%-50% of the total Hα emission of each galaxy. The integrated minimum Lyman continuum (Lyc) power required to sustain the DIG in each galaxy is enormous and can only easily be met by the ionizing output from massive star formation; the mechanical energy from supernovae and stellar winds falls short of that required by at least a factor of two. Our results support the hypothesis that the DIG is photoionized by Lyc photons which leak out of traditional H II regions, and suggest that the local H I column density plays a role in regulating the amount of leakage which can occur. This interpretation has profound implications for the derivation of global and radial star-formation rates based on Hα emission-line fluxes, leading to qualitatively and quantitatively different behaviors depending on whether the Hα emission from the DIG is included or not. The contribution of the diffuse Hα component to the total Hα emission; i.e., the diffuse fraction, in these galaxies is similar to values found in other galaxies with differing Hubble types and star-formation rates. The constancy of the diffuse fraction is rather unexpected and implies that the overall fraction of photons which can leak out of H II regions and ionize the ISM over large scales is relatively invariant from one galaxy to another. Publication: The Astronomical Journal Pub Date: June 1996 DOI: 10.1086/117961 Bibcode: 1996AJ....111.2265F Keywords: GALAXIES: SPIRAL; GALAXIES: ISM; HII REGIONS full text sources ADS | data products SIMBAD (9) NED (2)

A search for quasars and emission-line galaxies in the Sculptor region

view Abstract Citations (19) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A search for quasars and emission-line galaxies in the Sculptor region. Kunth, D. ; Sargent, W. L. W. Abstract A spectroscopic survey of emission-line candidates found in three objective-prism plates has been carried out resulting in 76 quasars, 28 emission-line galaxies, and three carbon stars. No new dwarf emission-line galaxies have been found with heavy-element abundances comparable or less than that of I ZW 18, about 1/30 the solar value. No galaxy belongs to the nearby Sculptor Group. The new sample of quasars doubles the number of known quasars in this region. Eighty percent have redshifts larger than 1.6 and were found from their Ly-alpha line emission. A preliminary study shows that quasar clustering is absent on any scale from 10 to 3500 Mpc, although a further critical analysis of the clustering investigation techniques is needed before any firm conclusion can be reached. Publication: The Astronomical Journal Pub Date: April 1986 DOI: 10.1086/114058 Bibcode: 1986AJ.....91..761K Keywords: Astronomical Spectroscopy; Carbon Stars; Galactic Radiation; Quasars; Astronomical Catalogs; Data Sampling; Emission Spectra; Red Shift; Spiral Galaxies; Astrophysics full text sources ADS | data products SIMBAD (109) NED (104)

The resolution of old red giant stars in the Sculptor group of galaxies

view Abstract Citations (46) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The resolution of old red giant stars in the Sculptor group of galaxies. Graham, J. A. Abstract Photographs are reproduced showing the resolution of the old red giant stars in the galaxies NGC 55 and NGC 300 which belong to the nearby Sculptor group of galaxies. The red magnitude of these stars is estimated to be 22.0 + or - 0.3 mag which corresponds to a visual magnitude of 23.0 mag. A comparison with NGC 205, a companion galaxy of M31, suggests an upper limit of 1.9 Mpc (modulus 26.4 mag) for the distances to NGC 55 and NGC 300. A similar degree of resolution is not seen in NGC 253 which is probably a more distant object. It is concluded that, like the members of the Local Group, the Sculptor galaxies are distributed over a large volume of space with NGC 55 and NGC 300 on the near side of the loose aggregate. Publication: The Astrophysical Journal Pub Date: January 1982 DOI: 10.1086/159575 Bibcode: 1982ApJ...252..474G Keywords: Astronomical Photography; Galactic Clusters; Image Resolution; Late Stars; Red Giant Stars; Stellar Magnitude; Galactic Evolution; Galactic Structure; Spatial Distribution; Stellar Evolution; Astrophysics full text sources ADS | data products SIMBAD (4) NED (3)