Browsing by Subject "h-ii regions"

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The Bolocam Galactic Plane Survey. VII. Characterizing The Properties Of Massive Star-Forming Regions
(2011-11) Dunham, Miranda K.; Rosolowsky, Erik; Evans, Neal J.; Cyganowski, Claudia; Urquhart, James S.; Dunham, Miranda K.; Evans, Neal J.
We present the results of a Green Bank Telescope survey of NH(3)(1,1), (2,2), (3,3) lines toward 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic longitudes in the inner Galaxy. We have detected the NH(3)(1,1) line toward 72% of our targets (456), demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas. We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH(3). The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms, with the number of sources peaking between R(Gal) similar to 4 and 5 kpc. We measure the physical properties of each source and find that depending on the distance, BGPS sources are primarily clumps, with some cores and clouds. We have examined the physical properties as a function of Galactocentric distance, and find a mean gas kinetic temperature of 15.6 K, and that the NH(3) column density and abundance decrease by nearly an order of magnitude between R(Gal) similar to 3 and 11 kpc. Comparing sources at similar distances demonstrates that the physical properties are indistinguishable, which suggests a similarity in clump structure across the Galactic disk. We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al. and Lada et al., and for massive star formation presented by Kauffmann et al. Forty-eight percent of our sample should be forming stars (including massive stars) with high efficiency, and 87% contain subregions that should be efficiently forming stars. Indeed, we find that 67% of the sample exhibit signs of star formation activity based on an association with a mid-infrared source.
The Broad-Lined Type Ic SN 2012ap And The Nature Of Relativistic Supernovae Lacking A Gamma-Ray Burst Detection
(2015-01) Milisavljevic, Dan; Margutti, R.; Parrent, Jerod T.; Soderberg, Alicia M.; Fesen, Robert A.; Mazzali, P.; Maeda, K.; Sanders, N. E.; Cenko, S. Bradley; Silverman, Jeffrey M.; Filippenko, Alexei V.; Kamble, A.; Chakraborti, S.; Drout, M. R.; Kirshner, Robert P.; Pickering, T. E.; Kawabata, K.; Hattori, T.; Hsiao, Eric Y.; Stritzinger, Maximillian D.; Marion, G. H.; Vinko, Jozsef; Wheeler, J. Craig; Silverman, Jeffrey M.; Marion, G. H.; Vinko, Jozsef; Wheeler, J. Craig
We present ultraviolet, optical, and near-infrared observations of SN 2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from -13 to +272 days past the B-band maximum of -17.4 +/- 0.5mag. The spectra are dominated by Fe II, OI, and Ca II absorption lines at ejecta velocities of nu approximate to 20,000 km s(-1) that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (nu greater than or similar to 27,000 km s(-1)). We use these observations to estimate explosion properties and derive a total ejecta mass of similar to 2.7 M-circle dot, a kinetic energy of similar to 1.0 x 10(52) erg, and a Ni-56 mass of 0.1-0.2 M-circle dot. Nebular spectra (t > 200 days) exhibit an asymmetric double-peaked [O I] lambda lambda 6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN 2012ap joins SN2009bb as another exceptional supernova that shows evidence for a central engine (e. g., black hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable observed properties including environmental metallicities of Z greater than or similar to Z(circle dot), moderate to high levels of host galaxy extinction (E(B - V) > 0.4mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] > 1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae.
The Fast And Furious Decay Of The Peculiar Type Ic Supernova 2005Ek
(2013-09) Drout, M. R.; Soderberg, Alicia M.; Mazzali, P. A.; Parrent, Jerod T.; Margutti, R.; Milisavljevic, Dan; Sanders, N. E.; Chornock, Ryan; Foley, Ryan J.; Kirshner, Robert P.; Filippenko, Alexei V.; Li, W.; Brown, Peter J.; Cenko, S. Bradley; Chakraborti, S.; Challis, Peter; Friedman, A.; Ganeshalingam, Mohan; Hicken, M.; Jensen, C.; Modjaz, M.; Perets, H. B.; Silverman, Jeffrey M.; Wong, D. S.; Silverman, Jeffrey M.
We present extensive multi-wavelength observations of the extremely rapidly declining Type Ic supernova (SN Ic), SN 2005ek. Reaching a peak magnitude of MR = -17.3 and decaying by similar to 3 mag in the first 15 days post-maximum, SN 2005ek is among the fastest Type I supernovae observed to date. The spectra of SN 2005ek closely resemble those of normal SN Ic, but with an accelerated evolution. There is evidence for the onset of nebular features at only nine days post-maximum. Spectroscopic modeling reveals an ejecta mass of similar to 0.3 M-circle dot that is dominated by oxygen (similar to 80%), while the pseudo-bolometric light curve is consistent with an explosion powered by similar to 0.03 M-circle dot of radioactive Ni-56. Although previous rapidly evolving events (e. g., SN 1885A, SN 1939B, SN 2002bj, SN 2010X) were hypothesized to be produced by the detonation of a helium shell on a white dwarf, oxygen-dominated ejecta are difficult to reconcile with this proposed mechanism. We find that the properties of SN 2005ek are consistent with either the edge-lit double detonation of a low-mass white dwarf or the iron-core collapse of a massive star, stripped by binary interaction. However, if we assume that the strong spectroscopic similarity of SN 2005ek to other SNe Ic is an indication of a similar progenitor channel, then a white-dwarf progenitor becomes very improbable. SN 2005ek may be one of the lowest mass stripped-envelope core-collapse explosions ever observed. We find that the rate of such rapidly declining Type I events is at least 1%-3% of the normal SN Ia rate.
Formaldehyde as a Probe of Physical Conditions in Dense Molecular Clouds
(1993-11) Mangum, Jeffrey G.; Wootten, Alwyn; Mangum, Jeffrey G.
We present a detailed analysis describing the utility of the formaldehyde (H2CO) molecule in the derivation of the kinetic temperature and spatial density within molecular clouds. Measurements of 13 transitions from both the ortho and para species of H2CO have been made toward a sample of 11 active star Formation regions. These H2CO transitions range in frequency from 21 1 to 365 GHz and in upper-state energy from 21 to 241 K. This range in excitation has allowed us to analyze H2CO sensitivity to both cool (T(K) less-than-or-similar 50 K) and warm (T(K) > 50 K) molecular material. Using a spherical large velocity gradient (LVG) model to solve for the excitation of H2CO, we analyze the sensitivity of several ortho- and para-H2CO transition intensity ratios to the kinetic temperature and spatial density within molecular clouds. Through this analysis we derive several ''rules of thumb'' which should be followed when measurements of a particular intensity ratio are used to calculate T(K) or n(H-2) in a molecular cloud. We find that for T(K) less than or similar 150 K and over ranges in H2CO Column density typical for most molecular clouds, several H2CO transition intensity ratios are excellent monitors of T(K) and n(H-2). Since the transitions whose relative intensities are sensitive to kinetic temperature can be measured using the same receiving system (and can in some cases be measured within the same spectrum), calibration uncertainties are minimized. We also present a detailed analysis of the uncertainties encountered in our modeling procedure, including the potential importance of infrared excitation. Using our measured H2CO radiation temperatures, we have constrained LVG model solutions for the kinetic temperature, spatial density, and H2CO Species column density in each of the sources in our sample. Our derived spatial densities are comparable to those estimated using other molecular tracers. In all of the regions in our sample, though, we measure kinetic temperatures greater than 50 K, significantly higher than previous estimates for many of these sources. Previous underestimation of T(K) is due to the use of tracers which are sensitive only to cool (T(K) less than or similar 50 K) gas. In particular, temperatures of 100 K or more occur both toward the cool young binary object IRAS 16293-2422 and toward the ''protostellar condensations'' FIR 4/FIR 5 in NGC 2024. Using our ortho- and para-H2CO measurements we have calculated the N(ortho-H2CO)/N(para-H2CO) ratio in several of the sources in our sample. Our measurements indicate that N(ortho-H2CO)/N(para-H2CO) < 3 for most of our sources. When combined with the relatively high kinetic temperature in these objects, this N(ortho-H2CO)/N(para-H2CO) ratio suggests that dust grains might play an active role in H2CO chemistry.
High-Resolution Mid-Infrared Spectroscopy Of NGC 7538 IRS 1: Probing Chemistry In A Massive Young Stellar Object
(2009-05) Knez, Claudia; Lacy, John H.; Evans, Neal J.; van Dishoeck, Ewine F.; Richter, Matthew J.; Knez, Claudia; Lacy, John H.; Evans, Neal J.
We present high-resolution (R = 75,000-100,000) mid-infrared spectra of the high-mass embedded young star IRS 1 in the NGC 7538 star-forming region. Absorption lines from many rotational states of C(2)H(2), (13)C(12)CH(2), CH(3), CH(4), NH(3), HCN, HNCO, and CS are seen. The gas temperature, column density, covering factor, line width, and Doppler shift for each molecule are derived. All molecules were fit with two velocity components between -54 and -63 km s(-1). We find high column densities (similar to 10(16) cm(-2)) for all the observed molecules compared to values previously reported and present new results for CH3 and HNCO. Several physical and chemical models are considered. The favored model involves a nearly edge-on disk around a massive star. Radiation from dust in the inner disk passes through the disk atmosphere, where large molecular column densities can produce the observed absorption line spectrum.
Lick Indices In The Thin And Thick Disks Of Edge-On Disk Galaxies
(2008-08) Yoachim, Peter; Dalcanton, Julianne J.; Yoachim, Peter
We have measured Lick index equivalent widths to derive luminosity weighted stellar ages and metallicities for thin-and thick-disk-dominated regions of nine edge-on disk galaxies with the ARC 3.5 m telescope at Apache Point Observatory. In all cases, the thick disks are confirmed to be old stellar populations, with typical ages between 4 and 10 Gyr. The thin disks are uniformly younger than the thick disks, and show strong radial age gradients, with the outer regions of the disks being younger than 1 Gyr. We do not detect any significant metallicity differences or alpha-element enhancement in the thick-disk stars compared to the thin disk, due to the insensitivity of the Lick indices to these differences at low metallicity. We compare these results to thick disks measured in other systems and to predictions from thick-disk formation models.
Mid-Infrared Photometry And Spectra Of Three High-Mass Protostellar Candidates At IRAS 18151-1208 And IRAS 20343+4129
(2008-02) Campbell, M. F.; Sridharan, T. K.; Beuther, H.; Lacy, John H.; Hora, J. L.; Zhu, Q.; Kassis, M.; Saito, M.; De Buizer, J. M.; Fung, S. H.; Johnson, L. C.; Lacy, John H.
We present arcsecond-scale mid-IR photometry ( in the 10.5 mu m N band and at 24.8 mu m), and low-resolution spectra in the N band ( R similar or equal to 100) of a candidate high-mass protostellar object ( HMPO) in IRAS 18151-1208 and of two HMPO candidates in IRAS 20343+4129, IRS 1 and IRS 3. In addition, we present high-resolution mid-IR spectra (R similar or equal to 80, 000) of the two HMPO candidates in IRAS 20343+4129. These data are fitted with simple models to estimate the masses of gas and dust associated with the mid-IR-emitting clumps, the column densities of overlying absorbing dust and gas, the luminosities of the HMPO candidates, and the likely spectral type of the HMPO candidate for which [Ne II] 12.8 mu m emission was detected ( IRAS 20343+4129 IRS 3). We suggest that IRAS 18151-1208 is a pre-ultracompact H II region HMPO, IRAS 20343+4129 IRS 1 is an embedded young stellar object with the luminosity of a B3 star, and IRAS 20343+4129 IRS 3 is a B2 ZAMS star that has formed an ultracompact H II region and disrupted its natal envelope.
A New Z=0 Metagalactic Ultraviolet Background Limit
(2011-02) Adams, Joshua J.; Uson, Juan M.; Hill, Gary J.; MacQueen, Phillip J.; Adams, Joshua J.; Hill, Gary J.; MacQueen, Phillip J.
We present new integral-field spectroscopy in the outskirts of two nearby, edge-on, late-type galaxies to search for the H alpha emission that is expected from the exposure of their hydrogen gas to the metagalactic ultraviolet background (UVB). Despite the sensitivity of the VIRUS-P spectrograph on the McDonald 2.7 m telescope to low surface brightness emission and the large field of view, we do not detect H alpha to 5 sigma upper limits of 6.4 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 7321 and of 25 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 1281 in each of the hundreds of independent spatial elements (fibers). We fit gas distribution models from overlapping 21 cm data of HI, extrapolate one scale length beyond the HI data, and estimate predicted H alpha surface brightness maps. We analyze three types of limits from the data with stacks formed from increasingly large spatial regions and compare to the model predictions: (1) single fibers, (2) convolution of the fiber grid with a Gaussian, circular kernel (10('') full width at half-maximum), and (3) the co-added spectra from a few hundred fibers over the brightest model regions. None of these methods produce a significant detection (>5 sigma) with the most stringent constraints on the Hi photoionization rate of Gamma(z = 0) < 1.7 x 10(-14) s(-1) in UGC 7321 and Gamma(z = 0) < 14 x 10(-14) s(-1) in UGC 1281. The UGC 7321 limit is below previous measurement limits and also below current theoretical models. Restricting the analysis to the fibers bound by the HI data leads to a comparable limit; the limit is Gamma(z = 0) < 2.3 x 10(-14) s(-1) in UGC 7321. We discuss how a low Lyman limit escape fraction in z similar to 0 redshift star-forming galaxies might explain this lower than predicted UVB strength and the prospects of deeper data to make a direct detection.
Physical Characteristics Of G331.5-0.1: The Luminous Central Region Of A Giant Molecular Cloud
(2013-09) Merello, Manuel; Bronfman, Leonardo; Garay, Guido; Nyman, Lars-Ake; Evans, Neal J.; Walmsley, C. Malcom; Merello, Manuel; Evans, Neal J.
We report molecular line and dust continuum observations toward the high-mass star-forming region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO(J = 1 -> 0) and (CO)-O-18(J = 1. 0) lines with NANTEN, while its central region was mapped in CS(J = 2 -> 1 and J = 5 -> 4) with SEST, and in CS(J = 7 -> 6) and (CO)-C-13(J = 3 -> 2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2 x 10(3)M(circle dot), molecular hydrogen density of 3.7 x 10(4) cm(-3), dust temperature of 32 K, and integrated luminosity of 5.7 x 10(5) L-circle dot, consistent with values found toward other massive star-forming dust clumps. The CS and (CO)-C-13 spectra show the presence of two velocity components: a high-velocity component at similar to-89 km s(-1), seen toward four of the clumps, and a low-velocity component at similar to-101 km s(-1) seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8 +/- 0.2 and 1.2 +/- 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s(-1) (FWHM) in CS(J = 7 -> 6). Observations of SiO(J = 7 -> 6 and J = 8. 7), and SO(J(K) = 8(8) -> 7(7) and J(K) = 8(7) -> 7(6)) lines provide estimates of the gas rotational temperature toward this outflow > 120 K and > 75 K, respectively.
The Properties of Massive, Dense Clumps: Mapping Surveys of HCN and CS
(2010-06) Wu, Jingwen; Evans, Neal J., II; Shirley, Yancy L.; Knez, Claudia; Evans, Neal J., II
We have mapped over 50 massive, dense clumps with four dense gas tracers: HCN J = 1-0 and 3-2; and CS J = 2-1 and 7-6 transitions. Spectral lines of optically thin H(13)CN 3-2 and C(34)S 5-4 were also obtained toward the map centers. These maps usually demonstrate single well-peaked distributions at our resolution, even with higher J transitions. The size, virial mass, surface density, and mean volume density within a well-defined angular size ( FWHM) were calculated from the contour maps for each transition. We found that transitions with higher effective density usually trace the more compact, inner part of the clumps but have larger linewidths, leading to an inverse linewidth-size relation using different tracers. The mean surface densities are 0.29, 0.33, 0.78, 1.09 g cm(-2) within FWHM contours of CS 2-1, HCN 1-0, HCN 3-2, and CS 7-6, respectively. We find no correlation of L(IR) with surface density and a possible inverse correlation with mean volume density, contrary to some theoretical expectations. Molecular line luminosities L'(mol) were derived for each transition. We see no evidence in the data for the relation between L'(mol) and mean density posited by modelers. The correlation between L'(mol) and the virial mass is roughly linear for each dense gas tracer. No obvious correlation was found between the line luminosity ratio and infrared luminosity, bolometric temperature, or the L(IR)/M(Vir) ratio. A nearly linear correlation was found between the infrared luminosity and the line luminosity of all dense gas tracers for these massive, dense clumps, with a lower cutoff in luminosity at L(IR) = 10(4.5) L(circle dot). The L(IR)-L'(HCN1-0) correlation agrees well with the one found in galaxies. These correlations indicate a constant star Formation rate per unit mass from the scale of dense clumps to that of distant galaxies when the mass is measured for dense gas. These results support the suggestion that starburst galaxies may be understood as having a large fraction of gas in dense clumps.
Simulating Cosmic Reionization And The Radiation Backgrounds From The Epoch Of Reionization
(2012) Shapiro, P. R.; Iliev, I. T.; Mellema, G.; Ahn, K.; Mao, Y.; Friedrich, M.; Datta, K.; Park, H.; Komatsu, E.; Fernandez, E.; Koda, J.; Bovill, M.; Pen, U. L.; Shapiro, Paul R.; Mao, Yi; Park, Hyunbae; Koda, Jun; Bovill, Mia
Large-scale reionization simulations are described which combine the results of cosmological N-body simulations that model the evolving density and velocity fields and identify the galactic halo sources, with ray-tracing radiative transfer calculations which model the nonequilibrium ionization of the intergalactic medium. These simulations have been used to predict some of the signature effects of reionization on cosmic radiation backgrounds, including the CMB, near-IR, and redshifted 21cm backgrounds. We summarize some of our recent progress in this work, and address the question of whether observations of such signature effects can be used to distinguish the relative contributions of galaxies of different masses to reionization.
Spatially Resolved Stellar, Dust, And Gas Properties Of The Post-Interacting Whirlpool Galaxy System
(2012-08) Cooper, Erin M.; Wilson, Christine D.; Foyle, Kelly; Bendo, George; Koda, Jin; Baes, Maarten; Boquien, Mederic; Boselli, Alessandro; Ciesla, Laure; Cooray, Asantha; Eales, Steve; Galametz, Maud; Lebouteiller, Vianney; Parkin, Tara; Roussel, Helene; Sauvage, Marc; Spinoglio, Luigi; Smith, Mathew W. L.; Cooper, Erin M.
Using infrared imaging from the Herschel Space Observatory, observed as part of the Very Nearby Galaxies Survey, we investigate the spatially resolved dust properties of the interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales of similar to 1 kpc. Spectral energy distribution modeling of the new infrared images in combination with archival optical and near-through mid-infrared images confirms that both galaxies underwent a burst of star formation similar to 370-480 Myr ago and provides spatially resolved maps of the stellar and dust mass surface densities. The resulting average dust-to-stellar mass ratios are comparable to other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at log(M-dust/M-star) = -2.5 +/- 0.2 and NGC 5195 at log(M-dust/M-star) = -3.5 +/- 0.3. The dust-to-stellar mass ratio is constant across NGC 5194 suggesting the stellar and dust components are coupled. In contrast, the mass ratio increases with radius in NGC 5195 with decreasing stellar mass density. Archival mass surface density maps of the neutral and molecular hydrogen gas are also folded into our analysis, revealing a fairly constant gas-to-dust mass ratio, 94 +/- 17 across the system. Somewhat surprisingly, we find the dust in NGC 5195 is heated by a strong interstellar radiation field (ISRF), over 20 times that of the ISRF in the Milky Way, resulting in relatively high characteristic dust temperatures (similar to 30 K). This post-starburst galaxy contains a substantial amount of low-density molecular gas and displays a gas-to-dust ratio (73 +/- 35) similar to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such high temperatures as there is no star formation in the galaxy and its active galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which exhibits only a modest enhancement in the amplitude of its ISRF.