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The placement of early-type dwarf galaxies (dSphs and dEs) with respect to the Potential Plane defined by pressure-supported late-type dwarf galaxies (dIs and BCDs) has been determined from surface brightness profiles. dEs and the most luminous dSphs lie on the Plane, suggesting that they emerged from late-type dwarfs that converted most of their gas into stars. However, there is a critical value of the potential at which dSphs start to fall systematically below the Plane, with the deviation growing as the potential becomes shallower. The displacements are attributed to depletion of baryons through gas loss, smaller galaxies having lost proportionately more gas. The critical potential corresponds to an escape velocity of 50 $\pm$ 8 km/s, which is what is expected for gas with a temperature of 13,000 $\pm$ 4,000 K, typical of a low-metallicity HII region. This suggests that photoionization was responsible for instigating the loss of gas by galaxies with potentials shallower than the critical value, with evacuation occurring over a few tens of millions of years. Extreme ratios of dynamical to luminous masses observed for the smallest dSphs are an artifact of mass loss. Because the efficiency with which gas was converted into stars was lower for dSphs with shallower potentials, there should be a minimum baryonic mass for a galaxy below which the stellar mass is negligible. Gross extrapolation of the trend of inferred gas masses with stellar masses suggests a value between 500 and 10,000 M$_\odot$. The corresponding dynamical mass is below 10$^6$ M$_\odot$., Comment: Accepted: MNRAS, 2019 March 19

It is demonstrated that the Local Sheet is both geometrically and dynamically distinct from the Local Supercluster and that the evolution of the Sheet and Local Group were probably interconnected. The Sheet is inclined by 8 degrees with respect to the Local Supercluster, and the dispersion of giant members about the mid-plane is only 230 kpc. A "Council of Giants" with a radius of 3.75 Mpc encompasses the Local Group, demarcating a clear upper limit to the realm of influence of the Local Group. The only two giant elliptical galaxies in the Sheet sit on opposite sides of the Council, raising the possibility that they have somehow shepherded the evolution of the Local Group. The position vector of the Andromeda galaxy with respect to the Milky Way deviates only 11 degrees from the Sheet plane and only 11 degrees from the projected axis of the ellipticals. The Local Group appears to be moving away from a ridge in the potential surface of the Council on a path parallel to the elliptical axis. Spin directions of the giants in the Council are distributed over the sky in a pattern which is very different from that of giants beyond, possibly in reaction to the central mass asymmetry that developed into the Local Group. By matching matter densities of Group and Council giants, the edge of the volume of space most likely to have contributed to the development of the Local Group is shown to be very close to where gravitational forces from the Local Group and the Council balance. The boundary specification reveals that the Local Sheet formed out of a density perturbation of very low amplitude (~10%), but that normal matter was incorporated into galaxies with relatively high efficiency (~40%). It appears that the development of the giants of the Local Sheet was guided by a pre-existing flattened framework of matter., Comment: 26 pages, 6 figures, 5 tables. MNRAS (2014), Advance Access. First published online: March 10, 2014

Studying the global evolution of spiral galaxies requires determining their overall chemical compositions. However, since spirals tend to possess gradients in their chemical compositions, determining their overall chemical abundances poses a challenge. In this study, the framework for a newly proposed method for determining the overall oxygen abundance of a disk is established. By separately integrating the absolute amounts of hydrogen and oxygen out to large radii, the cumulative oxygen abundance is shown to approach an asymptotic value. In this manner, a reliable account of the overall chemical state of a disk is revealed., Comment: 14 pages, 7 figures, 5 tables

Star-forming dwarfs are studied to elucidate the physical underpinnings of their fundamental plane. It is confirmed that residuals in the Tully-Fisher relation are correlated with surface brightness, but that even after accommodating the surface brightness dependence through the dwarf fundamental plane, residuals in absolute magnitude are far larger than expected from observational errors. Rather, a more fundamental plane is identified which connects the potential to HI line width and surface brightness. Residuals correlate with the axis ratio in a way which can be accommodated by recognizing the galaxies to be oblate spheroids viewed at varying angles. Correction of surface brightnesses to face-on leads to a correlation among the potential, line width, and surface brightness for which residuals are entirely attributable to observational uncertainties. The mean mass-to-light ratio of the diffuse component of the galaxies is constrained to be 0.88 +/- 0.20 in Ks. Blue compact dwarfs lie in the same plane as dwarf irregulars. The dependence of the potential on line width is less strong than expected for virialized systems, but this may be because surface brightness is acting as a proxy for variations in the mass-to-light ratio from galaxy to galaxy. Altogether, the observations suggest that gas motions are predominantly disordered and isotropic, that they are a consequence of gravity, not turbulence, and that the mass and scale of dark matter haloes scale with the amount and distribution of luminous matter. The tight relationship between the potential and observables offers the promise of determining distances to unresolved star-forming dwarfs to an accuracy comparable to that provided by the Tully-Fisher relation for spirals., Comment: 25 pages, including 9 figures and 5 tables

We present chemical abundances for planetary nebulae in M32, NGC 185, and NGC 205 based upon spectroscopy obtained at the Canada-France-Hawaii Telescope using the Multi-Object Spectrograph. From these and similar data compiled from the literature for other Local Group galaxies, we consider the origin and evolution of the stellar progenitors of bright planetary nebulae in galaxies where star formation ceased long ago. The ratio of neon to oxygen abundances in bright planetary nebulae is either identical to that measured in the interstellar medium of star-forming dwarf galaxies or at most changed by a few percent, indicating that neither abundance is significantly altered as a result of the evolution of their stellar progenitors. Several planetary nebulae appear to have dredged up oxygen, but these are the exception, not the rule. The progenitors of bright planetary nebulae typically enhance their original helium abundances by less than 50%. In contrast, nitrogen enhancements can reach factors of 100. However, nitrogen often shows little or no enhancement, suggesting that nitrogen enrichment is a random process. The helium, oxygen, and neon abundances argue that the typical bright planetary nebulae in all of the galaxies considered here are the progeny of stars with initial masses of approximately 1.5 Msun or less, based upon the nucleosynthesis predictions of current theoretical models. These models, however, are unable to explain the nitrogen enrichment or its scatter. Similar conclusions hold for the bright planetary nebulae in galaxies with ongoing star formation. Thus, though composition varies significantly, there is unity in the sense that the progenitors of typical bright planetary nebulae appear to have undergone similar physical processes. (Abridged), Comment: accepted for publication in the Astrophysical Journal

We present chemical abundances for planetary nebulae and H II regions in the Local Group dwarf irregular galaxy NGC 6822 based upon spectroscopy obtained at the Canada-France-Hawaii Telescope using the Multi-Object Spectrograph. From these and similar data compiled from the literature for planetary nebulae in the Magellanic Clouds, Sextans A, Sextans B, and Leo A, we consider the origin and evolution of the stellar progenitors of bright planetary nebulae in dwarf irregular galaxies. On average, the oxygen abundance observed in the bright planetary nebulae in these galaxies coincides with that measured in the interstellar medium, indicating that, in general, the bright planetary nebulae in dwarf irregulars descend primarily, though not exclusively, from stars formed in the relatively recent past. We also find that the ratio of neon to oxygen abundances in these bright planetary nebulae is identical to that measured in the interstellar medium, indicating that neither abundance is significantly altered as a result of the evolution of their stellar progenitors. We do find two planetary nebulae, that in Sextans A and S33 in NGC 6822, where oxygen appears to have been dredged up, but these are the exception rather than the rule. In fact, we find that even nitrogen is not always dredged up, so it appears that the dredge-up of oxygen is uncommon for the abundance range of the sample., Comment: accepted for publication in ApJ

We have obtained spectra of HII regions in the heavily obscured spiral galaxy Maffei 2. The observations have allowed for a determination of the Galactic extinction of this galaxy using a correlation between extinction and hydrogen column density observed among spirals. The technique reveals that the optical depth of Galactic dust at 1 micron obscuring Maffei 2 is tau1 = 2.017 +/- 0.211, which implies that A_V = 5.58 +/- 0.58 mag, significantly higher than observed for the giant elliptical Maffei 1 despite its similar latitude. For comparison, we apply the same technique to IC 342, a neighbouring spiral to Maffei 2 but with more moderate obscuration by Galactic dust, owing to its higher Galactic latitude. For this galaxy, we obtain tau1 = 0.692 +/- 0.066, which agrees within errors with the value of 0.639 +/- 0.102 derived from the reddening estimate of Schlegel et al. (1998, ApJ, 500, 525). We therefore adopt the weighted mean of tau1 = 0.677 +/- 0.056 for the extinction of IC 342, which implies that A_V = 1.92 +/- 0.16 mag. A new distance estimate for Maffei 2 of 3.34 +/- 0.56 Mpc is obtained from a self-consistent Tully-Fisher relation in I adjusted to the NGC 4258 maser zero-point. With our new measurement of M_I, Maffei 2 joins Maffei 1 and IC 342 as one of three giant members of the nearby IC 342/Maffei group of galaxies. We present the revised properties of all three galaxies based on the most accurate extinction and distance estimates to date, accounting for shifts in the effective wavelengths of broadband filters as this effect can be significant for highly reddened galaxies. The revised distances are consistent with what would be suspected for the Hubble Flow, making it highly unlikely that the galaxies interacted with the Local Group since the Big Bang., Comment: Accepted for publication in the Astrophysical Journal

A sample of 34 dwarf irregular galaxies in the Local Volume, most nearer than 5 Mpc, has been imaged in the near-infrared (NIR) in J and K_s at CFHT in Hawaii and OAN-SPM in Mexico. In CFHT images, stars brighter than M_Ks=-7.5 were resolved. In most cases, the resolved population represents less than 5% of the total NIR flux in K_s. Although exponential at large radii, surface brightness profiles for the unresolved component flatten in the centres. They can be fitted across the whole range of radii with a hyperbolic secant (sech) defined as a function of two parameters: the central surface brightness and the scale length of the exponential. Isophotal, total, and fitted sech magnitudes have been calculated for all galaxies for which the unresolved component was detected, along with semimajor axes. The scale length and the semimajor axes correlate linearly with absolute isophotal magnitude. The same is true for colors and the central brightness. More luminous dIs tend to be larger, redder and brighter in the centre. The Tully-Fisher relation shows considerable scatter, but residuals are tied to surface brightness. The galaxies appear to lie in a ``fundamental plane'' defined by the sech absolute magnitude, the sech central surface brightness, and the HI line-width. The rms of residuals in M_K is only 0.4 mag, which implies that the plane can be used to evaluate the distances of star-forming dwarfs. Color-magnitude diagrams are presented for 29 galaxies in which stars were resolved. Most show a finger centered around J-K_s=1 mag. In some cases, there is a red tail extending to J-K_s=2.5 mag. (Abstract slightly shortened)., Comment: Accepted for publication in AJ. Full version including figures available at http://aries.phys.yorku.ca/~ovidiuv/Paper2.ps.gz

Despite much work, the connection between dwarf elliptical galaxies (dEs) and dwarf irregulars (dIs) remains unclear. Recently, we found that the surface brightness profiles (SBPs) of dIs in the near-infrared can be well fitted with a hyperbolic secant (sech) function. From sech fits, a tight relationship was derived between the absolute magnitude, central surface brightness, and 21cm line widths, which amounts to a fundamental plane for dIs. Here we examine how closely dEs fit into the dI fundamental plane using published data for 22 dEs in the Virgo cluster and the Local Group. Over a 9 mag interval in absolute magnitude the dEs fall in the plane defined by the dIs. The outstanding overlap suggests more than a casual relationship between the two classes., Comment: To appear in the Proceedings of the IAU Colloquium 198, H. Jerjen & B. Binggeli

The measurement of chemical abundances in planetary nebulae in nearby galaxies is now relatively straightforward. The challenge is to use these chemical abundances to infer the chemical evolution of their host galaxies. At this point, our understanding of chemical evolution based upon planetary nebulae in galaxies without star formation is strongly coupled to our understanding of the relationship between the chemical abundances in stars and planetary nebulae in the Milky Way bulge. Supposing that the same relation holds in all systems where star formation ceased long ago, these systems follow a metallicity-luminosity relation that is displaced to higher chemical abundances compared to that found for dwarf irregular galaxies. A more efficient enrichment process appears to be required as part of the explanation for this shift, in addition to the inevitable fading of these galaxies., Comment: 12 pages, 4 figures, invited talk, Proceedings of the ESO Workshop on Planetary Nebulae beyond the Milky Way, held in Garching, Germany, 19-21 May 2004, conference proceedings will appear in in the Springer-Verlag series "ESO Astrophysics Symposia", eds. J. Walsh and L. Stanghellini

Quantitative information about variations in the background at J and K' are presented and used to develop guidelines for the acquisition and reduction of ground-based images of faint extended sources in the near-infrared, especially those which occupy a significant fraction of the field of view of a detector or which are located in areas crowded with foreground or background sources. Findings are based primarily upon data acquired over three photometric nights with the 3.6x3.6 arcmin CFHT-IR array on the Canada-France-Hawaii Telescope atop Mauna Kea. Although some results are specific to CFHT, overall conclusions should be useful in guiding observing and reduction strategies of extended objects elsewhere., Comment: Accepted for publication in PASP July 2004. 29 pages, including 2 tables and 9 figures

The impact of the cluster environment on the evolution of dwarf galaxies is investigated by comparing the properties of a sample of dwarf irregulars (dIs) in the Virgo Cluster with a control sample of nearby ("field") dIs having oxygen abundances derived from [O III]4363 measurements and measured distances from resolved stellar constituents. Spectroscopic data are obtained for H II regions in 11 Virgo dIs distributed in the central and outer regions of the cluster. To ensure that oxygen abundances are derived in a homogeneous manner, oxygen abundances for field and Virgo dIs are computed using the bright-line method and compared with abundances directly obtained from [O III]4363, where available. They are found to agree to within about 0.2 dex with no systematic offset. At a given optical luminosity, there is no systematic difference in oxygen abundance between the sample of Virgo dIs and the sample of nearby dIs. However, five of the eleven Virgo dIs exhibit much lower baryonic gas fractions than field dIs at comparable oxygen abundances. Using field dIs as a reference, a gas-deficiency index for dIs is constructed, making it possible quantitatively to identify which galaxies have lost gas. For the Virgo sample, some of the dwarfs are gas-deficient by a factor of 30. The gas-deficiency correlates roughly with the X-ray surface brightness of the intracluster gas. Ram-pressure stripping can best explain the observed gas-poor dIs in the cluster sample. Together with the lack of significant fading and reddening of the gas-poor dIs compared to gas-normal dIs, these observations suggest that the gas-poor dIs in Virgo have recently encountered the intracluster medium for the first time. Faded remnants of gas-poor dIs in Virgo will resemble bright dwarf ellipticals presently seen in the cluster core., Comment: Accepted, A.J.; 22 pgs. (emulateapj AASTeX 5.02), 28 jpg figures. Full paper w. incl. figures at http://www.mpia.de/homes/lee/paper2.ps.gz

We have obtained low- and high-resolution spectra of the core of the highly-reddened elliptical galaxy Maffei 1. From these data, we have obtained the first measurement of the Mg2 index, and have measured the velocity dispersion and radial velocity with improved accuracy. To evaluate the extinction, a correlation between the Mg2 index and effective V-I colour has been established for elliptical galaxies. Using a new method for correcting for effective wavelength shifts, we find A_V = 4.67 +/- 0.19 mag, which is lower by 0.4 mag than previously thought. To establish the distance, the Fundamental Plane for elliptical galaxies has been constructed in I. The velocity dispersion of Maffei 1, measured to be 186.8 +/- 7.4 km/s, in combination with modern wide-field photometry in I, leads to a distance of 2.92 +/- 0.37 Mpc. The Dn-sigma relation, which is independently calibrated, gives 3.08 +/- 0.85 Mpc and 3.23 +/- 0.67 Mpc from photometry in B and K`, respectively. The weighted mean of the three estimates is 3.01 +/- 0.30 Mpc. The distance and luminosity make Maffei 1 the nearest giant elliptical galaxy. The radial velocity of Maffei 1 is +66.4 +/- 5.0 km/s, significantly higher than the accepted value of -10 km/s. The Hubble distance corresponding to the mean velocity of Maffei 1, Maffei 2 and IC342 is 3.5 Mpc. Thus, it is unlikely that Maffei 1 has had any influence on Local Group dynamics.

In order to recognize environmental effects on the evolution of dwarf galaxies in clusters of galaxies, it is first necessary to quantify the properties of objects which have evolved in relative isolation. With oxygen abundance as the gauge of metallicity, two key diagnostics of the evolution of dwarf irregular galaxies in the field are re-examined: the metallicity-luminosity relationship and the metallicity-gas fraction relationship. Gas fractions are evaluated from the masses of luminous components only, i.e., constituents of the nucleogenetic pool. Results from new optical spectroscopy obtained for H II regions in five dwarf irregular galaxies in the Local Volume are incorporated into a new analysis of field dwarfs with [O III]4363 detections and good distances. The updated fit to the metallicity-luminosity relationship is consistent with results reported in the literature. The fit to the metallicity-gas fraction relation shows an excellent correlation consistent with expectations of the simple "closed box" model of chemical evolution. The simplest explanation consistent with the data is that flow rates are zero, although the observations allow for the possibility of modest flows. The derived oxygen yield is one-quarter of the value for the solar neighbourhood., Comment: v2: minor revisions after proofs; 25 pages (emulateapj AASTeX 5.02), 5 eps figures; A.J., in press, sched. Jan. 2003

We present optical spectroscopy of H {\sc ii} regions in the Local Group galaxy IC 10 and $UBVR$ photometry of foreground stars in three fields towards this galaxy. From these data, we find that the foreground reddening due to the Milky Way is $E(B-V)=0.77\pm 0.07 \mathrm{mag}$. We find that IC 10 contains considerable internal dust, which qualitatively explains the variety of reddening values found by studies of its different stellar populations. Based upon our foreground reddening, IC 10 has intrinsic photometric properties like those of a blue compact dwarf galaxy, and not those of a dwarf irregular. This result is consistent with much evidence that IC 10 is in the throes of a starburst that began at least $10 \mathrm{Myr}$ ago. We also report the discovery of a new WR star in the H {\sc ii} region HL111c.

We present the results of optical spectroscopy of a newly discovered H II region residing in the H I gas cloud located between the dwarf irregular galaxy UGC 7636 and the giant elliptical galaxy NGC 4472 in the Virgo Cluster. By comparing UGC 7636 with dwarf irregular galaxies in the field, we show that the H I cloud must have originated from UGC 7636 because (1) the oxygen abundance of the cloud agrees with that expected for a galaxy with the blue luminosity of UGC 7636, and (2) M_{H I}/L_B for UGC 7636 becomes consistent with the measured oxygen abundance of the cloud if the H I mass of the cloud is added back into UGC 7636. It is likely that tides from NGC 4472 first loosened the H I gas, after which ram-pressure stripping removed the gas from UGC 7636., Comment: 12 pages, 2 eps figures (AASTeX 5.0); accepted for publication in ApJ Letters

We present spectroscopy of planetary nebulae in M32 and in the bulge of M31 that we obtained with the MOS spectrograph at the Canada-France-Hawaii Telescope. Our sample includes 30 planetary nebulae in M31 and 9 planetary nebulae in M32. We also observed one H II region in the disk of M31. We detected [O III]$\lambda$4363 in 18 of the planetary nebulae, 4 in M32 and 14 in the bulge of M31. We use our line intensities to derive electron temperatures and oxygen abundances for the planetary nebulae., Comment: 17 pages, 12 figures, accepted by Astronomy & Astrophysics Supplement Series

We investigate the chemical properties of M32, the bulges of M31 and the Milky Way, and the dwarf spheroidal galaxies NGC 205, NGC 185, Sagittarius, and Fornax using previously published oxygen abundances for their planetary nebulae. Our principal result is that the mean stellar oxygen abundances for all of these galaxies correlate very well with their mean velocity dispersions. This implies that the balance between energy input from type II supernovae and the gravitational potential energy controls how far chemical evolution proceeds in bulges, ellipticals, and dwarf spheroidals. It appears that chemical evolution ceases once supernovae have injected sufficient energy that a galactic wind develops. All of the galaxies follow a single relation between oxygen abundance and luminosity, but the dwarf spheroidals have systematically higher [O/Fe] ratios than the other galaxies. Consequently, dynamically hot galaxies do not share a common star formation history nor need they share a common chemical evolution, despite attaining similar mean stellar oxygen abundances when forming similar stellar masses. The oxygen abundances support previous indications that the stars in higher luminosity ellipticals and bulges were formed on a shorter time scale than their counterparts in less luminous systems. We calibrate the Mg$_2$ index for dynamically hot galaxies as a function of observed age and oxygen abundance using the mean oxygen abundances from the planetary nebulae and the best age estimates available for the stars in M32 and the bulges of M31 and the Milky Way., Comment: 12 pages, 5 figures, accepted by Astronomy & Astrophysics

High signal-to-noise long-slit spectra have been obtained of the giant H II region NGC 2363 located in the dwarf SBm galaxy NGC 2366. A discovery of low-intensity broad spectral components (FWHM is approximately equal to 40 A or 2400 km/s) in the bright nebular lines H-alpha, H-beta, and forbidden O III is reported. The broad spectral components are detected over a large spatial extent (not less than 500 pc) centered on the nebula. Several mechanisms for broadening nebular lines are explored: stellar winds, Thomson scattering by hot gas, supernova remnants, and superbubble blowout. All mechanisms have problems. Superbubble blowout, which is the only known mechanism capable of accelerating interstellar gas over such a volume of space, does not appear consistent with the physical properties of the H II region NGC 2363 or with the nature of the host galaxy. It is concluded that the broad nebular lines are probably due to very high velocity gas whose origin is, at present, unknown.

Massive star formation in a low metallicity environment is investigated by studying the morphology of small HII regions in the Small Magellanic Cloud. A classification scheme based upon the symmetry of form in the light of H-alpha is proposed to make possible an examination of the properties of blister candidates with respect to nebulas embedded in a more uniform medium. A new diagnostic of size is developed to derive quantitative information about the ionized gas and ionizing stars. The asymmetrical surface-brightness distribution of many HII regions demonstrates that massive stars often form at the edge of dense neutral clouds. However, the existence of many symmetrical nebulas with similar sizes, luminosities, and surface brightnesses shows that massive star formation often occurs within these clouds. Nevertheless, the statistics of the two different forms indicate that the rate of massive star formation declines less steeply with radius across host clouds than in the Milky Way, suggesting that external triggering may play a larger role in initiating star formation.

A V-band polarimetric survey of stars associated with the Lagoon nebula was conducted. The data were combined with existing photometric and spectroscopic observations in order to investigate the alignment of magnetic field lines with identifiable symmetry axes and to evaluate the nature of dust in the immediate vicinity. Although stars are not in general highly polarized, electric vectors align with the minor axis of the Lagoon nebula, perpendicular to the major axis of the spatial distribution of massive stars. The observations indicate that the collapse of the molecular cloud progenitor was inhibited along directions perpendicular to magnetic field lines. Considering the low polarization efficiency and the high ratio of total to selective extinction, smaller grains of intranebular dust appear to have been destroyed.

Near-infrared spectroscopy at high altitude and low humidity has been carried out to accurately measure (Ar III) lambda 7136 and (S III) lambda 9069 in the extreme metal-poor dwarf irregular galaxy IZw18. The ratio of the abundance of argon to the abundance of sulfur is within about 0.2 dex of the value for the solar neighborhood. Since n(Ar)/n(S) appears to be a universal constant, the line ratio (AR III) lambda 7136/(S III) lambda 9069 may be a useful diagnostic of temperature in cool, metal-rich HII regions.

The region containing the Perseus flasher was observed for 5.4 h with the Exosat observatory. Upper limits to a point source with a steady X-ray flux were 2 x 10 to the -12th erg/sq cm s and 6 x 10 to the 12th erg/sq cm s. Upper limits to X-ray flashes of about 1 s duration were 4 x 10 to the 9th erg/sq cm s and 7 x 10 to the -10th erg/sq cm s. In view of the growing number of negative optical observations, it appears that either the optical flashes do not have a celestial origin, or that the flasher has a transient character and turns off for extended periods of time.