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First Detection of CO in a Low Surface Brightness Galaxy  [PDF]
K. O'Neil,P. Hofner,E. Schinnerer
Physics , 2000, DOI: 10.1086/317893
Abstract: We report on the first attempts at searching for CO in red low surface brightness galaxies, and the first detection of molecular gas in a low surface brightness (mu_B(0)_{obs} > 23 mag arcsec^{-2}) galaxy. Using the IRAM 30m telescope, CO(1-0) and CO(2-1) lines were searched for in four galaxies -- P06-1, P05-5, C05-3, & C04-2. In three of the galaxies no CO was detected, to T_{MB} ~ 1.8mK (at the 3 sigma level). In the fourth galaxy, P06-1, both lines were detected. Comparing our findings with previous studies shows P06-1 to have a molecular-to-atomic mass ratio considerably lower than is predicted using theoretical models based on high surface brightness galaxy studies. This indicates the N(H_2)/(int{T(CO)dv}) conversion factor for low surface brightness galaxies may currently be consistently underestimated by a factor of 3 - 20.
A CO J=3-2 map of M51 with HARP-B: Radial properties of the spiral structure  [PDF]
C. Vlahakis,P. van der Werf,F. P. Israel,R. P. J. Tilanus
Physics , 2013, DOI: 10.1093/mnras/stt841
Abstract: We present the first complete CO J=3-2 map of the nearby grand-design spiral galaxy M51 (NGC 5194), at a spatial resolution of ~600 pc, obtained with the HARP-B instrument on the James Clerk Maxwell Telescope. The map covers the entire optical galaxy disk and out to the companion NGC 5195, with CO J=3-2 emission detected over an area of ~9'x6' (~21x14 kpc). We describe the CO J=3-2 integrated intensity map and combine our results with maps of CO J=2-1, CO J=1-0 and other data from the literature to investigate the variation of the molecular gas, atomic gas and polycyclic aromatic hydrocarbon (PAH) properties of M51 as a function of distance along the spiral structure on sub-kpc scales. We find that for the CO J=3-2 and CO J=2-1 transitions there is a clear difference between the variation of arm and inter-arm emission with galactocentric radius, with the inter-arm emission relatively constant with radius and the contrast between arm and inter-arm emission decreasing with radius. For CO J=1-0 and HI the variation with radius shows a similar trend for the arm and inter-arm regions, and the arm-inter-arm contrast appears relatively constant with radius. We investigate the variation of CO line ratios (J=3-2/2-1, J=2-1/1-0 and J=3-2/1-0) as a function of distance along the spiral structure. Line ratios are consistent with the range of typical values for other nearby galaxies in the literature. The highest CO J=3-2/2-1 line ratios are found in the central ~1 kpc and in the spiral arms and the lowest line ratios in the inter-arm regions.We find no clear evidence of a trend with radius for the spiral arms but for the inter-arm regions there appears to be a trend for all CO line ratios to increase with radius. We find a strong relationship between the ratio of CO J=3-2 intensity to stellar continuum-subtracted 8mu PAH surface brightness and the CO J=3-2 intensity that appears to vary with radius.
Interstellar Gas in the NGC 4410 Galaxy Group  [PDF]
Beverly J. Smith
Physics , 2000, DOI: 10.1086/309448
Abstract: We present new radio continuum, 21 cm HI, and 2.6 mm CO data for the peculiar radio galaxy NGC 4410A and its companion NGC 4410B, and compare with available optical and X-ray maps. Our radio continuum maps show an asymmetric double-lobedstructure, with a high surface brightness lobe extending 3.6 arcmin (~100 kpc) to the southeast and a 6.2 arcmin (~180 kpc) low surface brightness feature in the northwest. Molecular gas is abundant in NGC 4410A, with M(H2) ~ 4 X 10^9 M(sun) (using the standard Galactic conversion factor), but is undetected in NGC 4410B. HI is less abundant, with M(HI) ~ 10^9 M(sun) for the pair. Our HI map shows a 3 X 10^8 M(sun) HI tail extending 1.7 arcmin (50 kpc) to the southeast of the pair, coincident with a faint optical tail and partially overlapping with the southeastern radio lobe. The HI tail is anti-coincident with a 2' (56 kpc) long X-ray structure aligned with a stellar bridge that connects the pair to a third galaxy. If this X-ray emission is associated with the group, there is 3 - 8 X 10^8 M(sun) of hot gas in this feature: either intracluster gas or shocked gas associated with the bridge. Our detection of abundant interstellar gas in this pair suggests that the distortions in this lobe map have been caused by the interstellar medium in this system. The interaction of the two galaxies and the subsequent motion of the interstellar medium in the system relative to the jet may have produced sufficient ram pressure to bend the radio jet. An alternative hypothesis is that the jet was distorted by ram pressure due to an intracluster medium, although the small radial velocity of NGC 4410A relative to the group and the lack of diffuse X-ray emission in the group makes this less likely unless the group is not virialized or is in the process of merging with another group.
Molecular Gas in 3C 293: The First Detection of CO Emission and Absorption in an F-R II Radio Galaxy  [PDF]
A. S. Evans,D. B. Sanders,J. A. Surace,J. M. Mazzarella
Physics , 1998, DOI: 10.1086/306717
Abstract: The first detection of CO emission in a Fanaroff-Riley Class II (i.e., edge-brightened radio morphology) radio galaxy is presented. Multi- wavelength (0.36-2.17 micron) imaging of 3C 293 shows it to be a disk galaxy with an optical jet or tidal tail extending towards what appears to be a companion galaxy 28 kpc away via a low surface brightness envelope. The molecular gas appears to be distributed in an asymmetric disk rotating around an unresolved continuum source, which is presumably emission from the AGN. A narrow (approx 60 km/s) absorption feature is also observed in the CO spectrum and is coincident with the continuum source. Using the standard CO conversion factor, the molecular gas mass is calculated to be 1.5x10^10 M_sun, several times the molecular gas mass of the Milky Way. The high concentration of molecular gas within the central 3 kpc of 3C 293, combined with the multiwavelength morphological peculiarities, support the idea that the radio activity has been triggered by a gas-rich galaxy-galaxy interaction or merger event.
Discovery of a Nearby Low-Surface-Brightness Spiral Galaxy  [PDF]
W. B. Burton,R. Braun,R. A. M. Walterbos,C. G. Hoopes
Physics , 1998, DOI: 10.1086/300700
Abstract: During the course of a search for compact, isolated gas clouds moving with anomalous velocities in or near our own Galaxy (Braun and Burton 1998 A&A, in press), we have discovered, in the data of the Leiden/Dwingeloo survey (Hartmann and Burton 1997, Atlas of Galactic Neutral Hydrogen, CUP) of Galactic hydrogen, the HI signature of a large galaxy, moving at a recession velocity of 282 km/s, with respect to our Galaxy. Deep multicolor and spectroscopic optical observations show the presence of star formation in scattered HII regions; radio HI synthesis interferometry confirms that the galaxy is rich in HI and has the rotation signature of a spiral galaxy; a submillimeter observation failed to detect the CO molecule. The radio and optical evidence combined suggest its classification as a low-surface-brightness spiral galaxy. It is located in close spatial and kinematic proximity to the galaxy NGC 6946. The newly-discovered galaxy, which we call Cepheus 1, is at a distance of about 6 Mpc. It is probably to be numbered amongst the nearest few LSB spirals.
Bimodality of Galaxy Disk Central Surface Brightness Distribution in the Spitzer 3.6 micron band  [PDF]
Jenny G. Sorce,Helene M. Courtois,Kartik Sheth,R. Brent Tully
Physics , 2013, DOI: 10.1093/mnras/stt768
Abstract: We report on measurements of the disk central surface brightnesses (mu0) at 3.6 microns for 438 galaxies selected by distance and absolute magnitude cutoffs from the 2350+ galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G), one of the largest and deepest homogeneous mid-infrared datasets of nearby galaxies. Our sample contains nearly 3 times more galaxies than the most recent study of the mu0 distribution. We demonstrate that there is a bimodality in the distribution of mu0. Between the low and high surface brightness galaxy regimes there is a lack of intermediate surface brightness galaxies. Caveats invoked in the literature from small number statistics to the knowledge of the environmental influences, and possible biases from low signal to noise data or corrections for galaxy inclination are investigated. Analyses show that the bimodal distribution of mu0 cannot be due to any of these biases or statistical fluctuations. It is highly probable that galaxies settle in two stable modes: a dark matter dominated mode where the dark matter dominates at all radii - this gives birth to low surface brightness galaxies - and a baryonic matter dominated mode where the baryons dominate the dark matter in the central parts - this gives rise to the high surface brightness disks. The lack of intermediate surface brightness objects suggests that galaxies avoid (staying in) a mode where dark matter and baryons are co-dominant in the central parts of galaxies.
Further Discoveries of 12CO in Low Surface Brightness Galaxies  [PDF]
K. O'Neil,E. Schinnerer,P. Hofner
Physics , 2003, DOI: 10.1086/373895
Abstract: Using the IRAM 30m telescope we have obtained seven new, deep CO J(1-0) and J(2-1) observations of low surface brightness (LSB) galaxies. Five of the galaxies have no CO detected to extremely low limits (0.1-0.4 K km/s at J(1-0)), while two of the galaxies, UGC 01922 and UGC 12289, have clear detections in both line transitions. When these observations are combined with all previous CO observations taken of LSB systems, we compile a total of 34 observations, in which only 3 galaxies have had detections of their molecular gas. Comparing the LSB galaxies with and without CO detections to a sample of high surface brightness (HSB) galaxies with CO observations indicates that it is primarily the low density of baryonic matter within LSB galaxies which is causing their low CO fluxes. Finally, we note that one of the massive LSB galaxies studied in this project, UGC 06968 (a Malin-1 `cousin'), has upper limits placed on both M_H2 and M_H2/M_HI which are 10-20 times lower than the lowest values found for any galaxy (LSB or HSB) with similar global properties. This may be due to an extremely low temperature and metallicity within UGC 06968, or simply due to the CO distribution within the galaxy being too diffuse to be detected by the IRAM beam.
The Molecular ISM in Low Surface Brightness Disk Galaxies  [PDF]
Chris Mihos,Marco Spaans,Stacy McGaugh
Physics , 1998,
Abstract: We present models for the interstellar medium in disk galaxies. In particular, we investigate whether the ISM in low surface brightness galaxies can support a significant fraction of molecular gas given their low metallicity and surface density. It is found that the abundance and line brightness of CO in LSB galaxies is small and typically below current observational limits. Still, depending on physical details of the ISM, the fraction of gas in the form of molecular hydrogen can be significant in the inner few kpc of a low surface brightness galaxy. This molecular gas would be at temperatures of $\sim$ 30 -- 50 K, rather higher than in high surface brightness galaxies. These results may help explain the star forming properties and inferred evolutionary history of LSB galaxies.
Galaxy Selection and the Surface Brightness Distribution  [PDF]
S. S. McGaugh,G. D. Bothun,J. M. Schombert
Physics , 1995, DOI: 10.1086/117543
Abstract: Optical surveys for galaxies are biased against the inclusion of low surface brightness (LSB) galaxies. Disney (1976) suggested that the constancy of disk central surface brightness noticed by Freeman (1970) was not a physical result, but instead was an artifact of sample selection. Since LSB galaxies do exist, the pertinent and still controversial issue is if these newly discovered galaxies constitute a significant percentage of the general galaxy population. In this paper, we address this issue by determining the space density of galaxies as a function of disk central surface brightness. Using the physically reasonable assumption (which is motivated by the data) that central surface brightness is independent of disk scale length, we arrive at a distribution which is roughly flat (i.e. approximately equal numbers of galaxies at each surface brightness) faintwards of the Freeman (1970) value. Brightwards of this, we find a sharp decline in the distribution which is analogous to the turn down in the luminosity function at $L^*$. An intrinsically sharply peaked ``Freeman Law'' distribution can be completely ruled out, and no Gaussian distribution can fit the data. Low surface brightness galaxies (those with central surface brightnesses fainter than $22~B\sb$) comprise $\gtrsim 1/2$ the general galaxy population, so a representative sample of galaxies at $z = 0$ does not really exist at present since past surveys have been insensitive to this component of the general galaxy population.
The Star Clusters in the Starburst Irregular Galaxy NGC 1569  [PDF]
D. A. Hunter,R. W. O'Connell,J. S. Gallagher,T. A. Smecker-Hane
Physics , 2000, DOI: 10.1086/316810
Abstract: We examine star clusters in the irregular, starburst galaxy NGC 1569 from HST images. In addition to the two known super star clusters, we identify 45 other clusters that are compact but resolved. Integrated UVI colors of the clusters span a large range, and suggest that ages range from 3 Myrs to 1 Gyr. However, most of the clusters were formed at the tail end of the recent starburst. Numerous clusters in addition to the know super star clusters are similar in luminosity to a small globular cluster. We examined the radial surface brightness of four of the clusters. Their half-light radii and core radii are in the range observed in present-day globular clusters. Therefore, conditions that produced the recent starburst have also been those necessary for producing compact, bright star clusters. We examine resolved stars in the outer parts of the two super star clusters. Cluster A is dominated by bright blue stars with a small population of red supergiants. Sub-components A1 and A2 have similar colors and a two-dimensional color map does not offer evidence that one component is dominated by red supergiants and the other not. The contradiction of the presence of red super- giants with Wolf-Rayet stars may instead not be a contradiction at all since there coexistence in a coeval population is not inconsistent with the evolution of massive stars. Cluster B is dominated by red supergiants, and this is confirmed by the presence of the stellar CO absorption feature in an integrated spectrum. The various age indicators are consistent with a picture in which cluster B is of order 10--20 Myrs old, and cluster A is >4-5 Myrs old.
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