[en] The implications of the surface-brightness (SB) distribution of observed disk galaxies are explored, reviewing the results of recent investigations. Topics addressed include the SBs of catalog galaxies, proper measurements of SB, searches for new low-SB objects, and the importance of low-SB galaxies rich in H I for theoretical models of star formation. Key theoretical questions are listed, and tentative answers are given along with recommendations for further observations. 30 references

[en] Narrow-band (H alpha and (NII)) charge coupled device (CCD) images of elliptical galaxies suspected of having cooling flows are discussed. Researchers find evidence of optical emission from cool gas which is most likely associated with a cooling flow. At least 4 galaxies (NGC 3998, NGC 4203, NGC 4550 and NGC 4697) show emission of (NII) and/or H alpha within the central 20 seconds, a fraction consistent with results from Phillips et al. (1987) and Caldwell (1984). In these four, (NII) lambda 6584A emission is stronger than H alpha (which is often in absorption e.g., as seen in long slit spectra of NGC4697). From long slit spectra of these galaxies, Deustua and Teske (1989) infer electron densities, N sub e, of order 1.2x10 to the 3rd power cm(-3) assuming T = 10 to the 4th power K for the optically emitting gas. NGC 2685, NGC 3489 appear to have emission in (NII); NGC 4636 may also, but, is difficult to see in the data (Demoulin-Ulrich, Butcher and Boksenberg (1984) did not see emission from this galaxy). NGC 4472, NGC 4473, NGC 4365, NGC 4638 and NGC 4649 show no emission

[en] H-alpha photometric observations of the face-on Sc spiral galaxy NGC 628, obtained using 10-nm-bandwidth filters and a CCD detector on the 1.5-m Palomar telescope during October 1985, are reported and analyzed. Absolute luminosities are determined for 183 bright H II regions, and it is estimated that they contain clusters of about 100 young ionizing stars on average. Two theoretical models are constructed to explain the observed H II region luminosity function: in model (1) clusters differ only in the mass of gas involved in high-mass star formation and stellar evolution is ignored, while in model (2) clusters differ only in their state of evolution from initially identical conditions. Although both (1) and (2) can fit the observations, physical arguments are presented favoring (2), which also permits estimation of the slope of the massive-star initial mass function (near the Salpeter value of 2.35), the O-star formation rate (about 0.004/yr), the rate of type II SN (about 0.01/yr), and the number of WR stars in NGC 628 (about 800). 28 refs

[en] Optical and radio spectroscopic observations are presented for Malin 1, a galaxy with an extremely low surface brightness disks with an enormous mass of neutral hydrogen, and a low-luminosity Seyfert nucleus. The characteristics of Malin 1 are described and compared with normal disk galaxies. It is suggested that Malin 1 is an unevolving disk galaxy where the surface mass density is so low that the chemical composition and mass fraction in gas change very slowly over Hubble time. The results imply that large and massive H I disks may have formed as early as z = 2 and remained quiescent to the present day. 74 refs

[en] Throughout history, observations of the motions of objects in the Universe have provided the foundation for various cosmological models. In many cases, the invoked causes of the observed motion appeal to mysterious elements. Indeed, the very first test motion was that of the retrograde motion of Mars, which lead to a required epicycle to save the model (e.g., Ptolemy's unmoving Earth). By the early 1840s, from approximately 50 years of orbital data (since its 1789 discovery) it was apparent that Uranus was disobeying the Newtonian rules in its orbit and speculation mounted that a 'large unseen mass' was perturbing the orbit. Using Uranus as a test particle then yields the first notion of dark matter (DM). Alas, it was not DM but merely Neptune, discovered in September 1846. By 1859 enough data had been gathered to reveal that Mercury is also not obeying Newtonian physics but rather revealing curved space-time. The continuation of this history is now set in scales larger than the Solar System. Observations suggest two basic choices: (i) gravity is fully understood and Newton's second law is invariant (except in very strong gravity) and observed motions on galactic scales require the existence of DM (a currently unproven 'epicycle') or (ii) Newton's second law can be modified (e.g., MOND) in certain low acceleration scale environments. In this contribution we discuss the case for and against MOND on various scales and conclude that neither MOND nor our current cosmology (ΛCDM) consistently explain all observed phenomena. In general, MOND works much better on small scales than ΛCDM but encounters difficulties on large scales. Moreover, the nature of the acoustic power spectrum of the CMB now pretty clearly shows that a fully baryonic Universe is ruled out, thus necessitating some DM component. But this should not diminish the consideration of MOND as its introduced acceleration scale; a_o is fully consistent with the observed structural properties of galaxies in a way that the DM halo paradigm cannot match. Indeed, despite many attempts to falsify MOND, it has always come back from its proclaimed death to provide unique insights into the gravitational nature of galaxies, consistently raising the specter that our current understanding of gravity acting over large spatial scales may be flawed. (author)

[en] Because the fraction of dark matter in spiral galaxies varies with luminosity, or for a number of other possible reasons, the relation between infrared luminosity and velocity width has previously been shown to be nonlinear. The relation between surface brightness and velocity width is now demonstrated to be nonlinear also. When these nonlinearities are taken into account, an apparent trend in surface brightness of cluster spirals with redshift is shown to be spurious. Apparent correlations of surface brightness and slope on cluster richness and cluster velocity dispersion also disappear. Neither this effect, nor an apparent trend in slope of the infrared Tully-Fisher relation with Hubble type, in themselves imply that the Tully-Fisher relation depends on the environment in which galaxies are located. 26 refs

[en] The detection of an optical counterpart to the large H I cloud recently discovered by Giovanelli and Haynes (1989) in the Local Supercluster is reported. The peak of the H I flux corresponds to a low surface brightness, dwarf irregular galaxy. The counterpart was discovered on a photographically amplified image from the UK Schmidt Telescope, and its maximum extent is 180 arcsecs at the 27 mag/sq arcsec isotope. The H I and optical data may be explained by a pair of LSB dwarf irregular galaxies that have similar velocities. Some star formation appears to be taking place in this system, but the H I column density is below the threshold for extensive star formation. A kinematic study is required to determine the total mass. This galaxy is similar to other LSB dwarfs and dI pairs which have enormous mass-to-light ratios and H I sizes far in excess of the optical scale length. 25 refs

[en] Photometry and kinematics are presented for a sample of objective prism selected carbon stars toward the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R exp 1/4 density profile for the Galactic halo. This density profile can be traced to about 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yields an effective radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + or - 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data. 33 refs

[en] We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey sample based on 5-15 μm low-resolution spectra obtained with the Infrared Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for the galaxies in the sample, FEE_λ, defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the FEE_λ varies from one galaxy to another, but we can identify three general types of FEE_λ: one where FEE_λ is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7 μm. More than 30% of the galaxies have a median FEE_λ larger than 0.5, implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of FEE in their warm dust continuum (0 ∼< FEE_13.2μm ∼< 0.85). The large values of FEE_13.2μm that we find in many LIRGs suggest that the extended component of their MIR continuum emission originates in scales up to 10 kpc and may contribute as much as the nuclear region to their total MIR luminosity. The mean size of the LIRG cores at 13.2 μm is 2.6 kpc. However, once the IR luminosity of the systems reaches the threshold of L_IR ∼ 10^11.8 L_sun, slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with FEE_13.2μm ∼< 0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5 kpc. Furthermore, our analysis indicates that the compactness of systems with L_IR ∼> 10^11.25 L_sun strongly increases in those classified as mergers in their final stage of interaction. The FEE_13.2μm is also related to the contribution of an active galactic nucleus (AGN) to the MIR emission. Galaxies which are more AGN dominated are less extended, independently of their L_IR. We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f_60μm/f_100μm) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel Space Telescope.

[en] An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z = 0.036 merging galaxy system II Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L_IR/L_sun) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 μm and 6.2 μm polycyclic aromatic hydrocarbon emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M_sun yr^-1 and >45 M_sun yr^-1, respectively. Finally, the high-resolution B-, I-, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations-one with an age of 1-5 Myr and one with an age of 20-500 Myr, reddened by 0-2 mag of visual extinction. The masses of these clusters span a range between 10⁶ and 10⁸ M_sun. This starburst source is reminiscent of the extranuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the entire system.