We search for evidence of diffuse Ly alpha emission from extended neutral hydrogen surrounding Ly alpha emitting galaxies (LAEs) using deep narrow-band images of the Extended Chandra Deep Field ...South. By stacking the profiles of 187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and carefully performing low-surface brightness photometry, we obtain mean surface brightness maps that reach 9.9, 8.7, and 6.2 x 10 super(-19) erg cm super(-2) s super(-1) arcsec- super(2) in the emission line. We undertake a thorough investigation of systematic uncertainties in our surface brightness measurements and find that our limits are 5-10 times larger than would be expected from Poisson background fluctuations; these uncertainties are often underestimated in the literature. At z ~ 3.1, we find evidence for extended halos with small-scale lengths of 5-8 kpc in some but not all of our sub-samples. We demonstrate that sub-samples of LAEs with low equivalent widths and brighter continuum magnitudes are more likely to possess such halos. At z ~ 2.1, we find no evidence of extended Ly alpha emission down to our detection limits. Through Monte-Carlo simulations, we also show that we would have detected large diffuse LAE halos if they were present in our data sets. We compare these findings to other measurements in the literature and discuss possible instrumental and astrophysical reasons for the discrepancies.
We investigate the possible progenitors of the planetary nebulae (PNs) that populate the top 0.5 mag of the O III l5007 planetary nebula luminosity function (PNLF). We show that the absolute ...luminosity of the PNLF cutoff demands that the central stars of these most luminous PNs be 0.6 M sub( )and that such high-mass PN cores must exist in every galaxy. We also use the bolometric luminosity-specific PN number density to show that in early-type galaxies, O III-bright PNs are relatively rare, with only 610% of stars evolving to these bright magnitudes. We demonstrate that the combination of these two facts implies that either all early-type systems contain a small, smoothly distributed component of young ( 1 Gyr old) stars or that another mechanism exists for creating high core mass PNs. We argue that binary star evolution is this second mechanism and demonstrate that blue stragglers have the appropriate core properties and number density to explain the observations. We discuss the implications of this alternative mode of stellar evolution and speculate on how coalesced binaries might affect the use of PNs for measuring a galaxy's star formation history and chemical evolution.
The Planetary Nebula System of M33 Ciardullo, Robin; Durrell, Patrick R; Laychak, Mary Beth ...
The Astrophysical journal,
10/2004, Letnik:
614, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report the results of a photometric and spectroscopic survey for planetary nebulae (PNs) over the entire body of the Local Group spiral galaxy M33. We use our sample of 152 PNs to show that the ...bright end of the galaxy's O III 5007 planetary nebula luminosity function (PNLF) has the same sharp cutoff seen in other galaxies. The apparent magnitude of this cutoff, along with the IRAS DIRBE foreground extinction estimate of E(B - V) = 0.041, implies a distance modulus for the galaxy of (m - M) sub(0) = 24.86 (0.94 Mpc). Although this value is 15% larger than the galaxy's Cepheid distance, the discrepancy likely arises from differing assumptions about the system's internal extinction. Our photometry, which extends more than 3 mag down the PNLF, also reveals that the faint end of M33's PNLF is nonmonotonic, with an inflection point 2 mag below the PNLF's bright limit. We argue that this feature is due to the galaxy's large population of high core mass planetaries and that its amplitude may eventually be a useful diagnostic for studies of stellar populations. Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN population rotates along with the old disk, with a small asymmetric drift of 10 km s super(-1). Remarkably, the population's line-of-sight velocity dispersion varies little over 4 optical disk scale lengths, with sub(rad) 20 km s super(-1). We show that this is due to a combination of factors, including a decline in the radial component of the velocity ellipsoid at small galactocentric radii and a gradient in the ratio of the vertical to radial velocity dispersion. We use our data to derive the dynamical scale length of M33's disk and the disk's mass-to-light ratio. Our most likely solution suggests that the surface mass density of M33's disk decreases exponentially, but with a scale length that is 2.3 times larger than that of the system's IR luminosity. The large scale length also implies that the disk's V-band mass-to-light ratio changes from M/L sub(V) 0.3 in.
The patients in Glover and colleagues' study received hyperbaric oxygen after a median of 42 months after radiotherapy, a delay much longer than in other published series. Since chronic radiation ...tissue injury is, in part, a progressive fibroproliferative process, it's likely that treatment must be initiated before a certain threshold of scarring has occurred for success.
We have used the Hubble Space Telescope's Advanced Camera for Surveys (ACS) to detect and measure 65300 stars in a single intracluster field in the Virgo Cluster. By performing F606W and F814W ...photometry on these stars, we have determined their metallicity distribution function and constrained the types of stars present in this portion of Virgo's intracluster space. Based on the small number of stars detected that were brighter than the red giant branch (RGB) tip, we suggest that in this region, Virgo's intracluster stars are mostly old ( 10 Gyr). Through analysis of the RGB stars themselves, we determine that the population contains the full range of metallicities probed (-2.3 , M/H , 0.0). We also present evidence that the younger (,10 Gyr) component of the population is more metal-rich, with M/H > -0.5. The spatial distribution of the most metal-poor stars in the field shows significantly more structure than that of the metal-rich stars, indicating that the intracluster population is not well mixed. We discuss the implications that these observations have for the production of intracluster stars and the dynamical evolution of the Virgo Cluster.
We report the results of an O III l5007 survey for PNe in five galaxies that were hosts of well-observed SNe Ia: NGC 524, NGC 1316, NGC 1380, NGC 1448, and NGC 4526. The goals of this survey are to ...better quantify the zero point of the maximum magnitude--decline rate relation for SNe Ia and to validate the insensitivity of Type Ia luminosity to parent stellar population using the host galaxy Hubble type as a surrogate. We detected a total of 45 PN candidates in NGC 1316,44 candidates in NGC 1380, and 94 candidates in NGC 4526. From these data and the empirical planetary nebula luminosity function (PNLF), we derive distances of 17.9 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(8) sub(9), 16.1 super(+) sub(-) super(0) sub(1) super(.) sub(.) super(8) sub(1), and 13.6 super(+) sub(-) super(1) sub(1) super(.) sub(.) super(3) sub(2) Mpc, respectively. Our derived distance to NGC 4526 has a lower precision due to the likely presence of Virgo intracluster PNe in the foreground of this galaxy. In NGC 524 and NGC 1448 we detected no PN candidates down to the limiting magnitudes of our observations. We present a formalism for setting realistic distance limits in these two cases and derive robust lower limits of 20.9 and 15.8 Mpc, respectively. After combining these results with other distances from the PNLF, Cepheid, and surface brightness fluctuation distance indicators, we calibrate the optical and NIR relations for SNe Ia and find mat the Hubble constants derived from each of the three methods are broadly consistent, implying that the properties of SNe Ia do not vary drastically as a function of stellar population. We determine a preliminary Hubble constant of H sub(0) = 77c3 (random) c 5 (systematic) km s super(-1) Mpc super(-1) for the PNLF, although more nearby galaxies with high-quality observations are clearly needed.
Mr. Richard Clarke presents in this Journal his arguments against continued application of hyperbaric oxygen (HBO2) therapy to the pre-extraction neoadjuvant treatment or the treatment of frank ...mandibular ORN. In the same article he advocates a promising renewed interest in HBO2 as a radiosensitizer. Arguments against HBO2 prior to extractions are based on several papers which consistently include low-risk patients. The just-released HOPON trial reports a negative pre-extraction outcome for HBO2, but patients were enrolled with radiation doses as low as 50Gy. For advanced mandibular necrosis (Marx Stage III) requiring resection, fibular free flap reconstruction is advocated. A high complication rate with free flaps is acknowledged but the magnitude of these complications is not discussed. A cost savings for this procedure is suggested, but no mention is made of the typical cost of the procedure ($90,000) or the requirement of a typical one-week hospital stay, including an initial one or two days in the ICU. Nor is mention made of the very low rate of subsequent dental rehabilitation. The success reported by Delainian, et al. employing pentoxifylline, Vitamin E and sometimes a bisphosphonate is equated to the four decades of HBO2 success with the Marx protocol for Stage I and II ORN. In the phase II trial by Delainian (not randomized) six of her 54 patients died secondary to sepsis, and she graded patients as complete responders if 5mm or less bone was exposed. Even at entry patients had an average of only 1.7 cm exposed bone and treatment was prolonged (16 + or -9 months). Any cost comparison studies will have to account for the indirect expenses of this prolonged treatment including lost productivity.
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