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Abstract
The detailed morphology of the interstellar medium (ISM) in the central kiloparsec of galaxies is controlled by pressure and gravitation. The combination of these forces shapes both circumnuclear star formation and the growth of the central, supermassive black hole. We present visible and near-infrared Hubble Space Telescope images and color maps of 123 nearby galaxies that show the distribution of the cold ISM, as traced by dust, with excellent spatial resolution. These observations reveal that nuclear dust spirals are found in the majority of active and inactive galaxies and they possess a wide range in coherence, symmetry, and pitch angle. We have used this large sample to develop a classification system for circumnuclear dust structures. In spite of the heterogeneous nature of the complete sample, we only find symmetric, two-arm nuclear dust spirals in galaxies with large-scale bars, and these dust lanes clearly connect to dust lanes along the leading edges of the large-scale bars. Not all dust lanes along large-scale bars form two-arm spirals, however, and several instead end in nuclear rings. We find that tightly wound, or low pitch angle, nuclear dust spirals are more common in unbarred galaxies than barred galaxies. Finally, the extended narrow-line region in several of the active galaxies is well resolved. The connection between the ionized gas and circumnuclear dust lanes in four of these galaxies provides additional evidence that a significant fraction of their extended narrow-line region is ambient gas photoionized in situ by the active nucleus. In a future paper we will use our classification system for circumnuclear dust to identify differences between active and inactive galaxies, as well as barred and unbarred galaxies, in well-matched subsamples of these data.
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Abstract
The detailed morphology of the interstellar medium (ISM) in the central kiloparsec of galaxies is controlled by pressure and gravitation. The combination of these forces shapes both circumnuclear star formation and the growth of the central, supermassive black hole. We present visible and near-infrared Hubble Space Telescope images and color maps of 123 nearby galaxies that show the distribution of the cold ISM, as traced by dust, with excellent spatial resolution. These observations reveal that nuclear dust spirals are found in the majority of active and inactive galaxies and they possess a wide range in coherence, symmetry, and pitch angle. We have used this large sample to develop a classification system for circumnuclear dust structures. In spite of the heterogeneous nature of the complete sample, we only find symmetric, two-arm nuclear dust spirals in galaxies with large-scale bars, and these dust lanes clearly connect to dust lanes along the leading edges of the large-scale bars. Not all dust lanes along large-scale bars form two-arm spirals, however, and several instead end in nuclear rings. We find that tightly wound, or low pitch angle, nuclear dust spirals are more common in unbarred galaxies than barred galaxies. Finally, the extended narrow-line region in several of the active galaxies is well resolved. The connection between the ionized gas and circumnuclear dust lanes in four of these galaxies provides additional evidence that a significant fraction of their extended narrow-line region is ambient gas photoionized in situ by the active nucleus. In a future paper we will use our classification system for circumnuclear dust to identify differences between active and inactive galaxies, as well as barred and unbarred galaxies, in well-matched subsamples of these data.
View Full Publication open_in_new
Abstract
We present the first detailed X-ray observations of optically selected clusters at high redshift. Two clusters, Cl 1324 + 3011 at z = 0.76 and Cl 1604 + 4304 at z = 0.90, were observed with XMM-Newton. The optical center of each cluster is coincident with an extended X-ray source whose emission is detected out to a radius of similar to0.5 h(70)(-1) Mpc. The emission from each cluster appears reasonably circular, with some indication of asymmetries and more complex morphologies. Similar to other optically selected clusters at redshifts of z greater than or similar to0.4, both clusters are modest X-ray emitters with bolometric luminosities of only L-X(bol) = (1.4-2.0) x 10(44) h(70)(-2) ergs s(-1). We measure gas temperatures of T = 2.88(-0.49)(+0.71) keV for Cl 1324 + 3011 and 2.51(-0.69)(+1.05) keV for Cl 1604 + 4304. The X-ray properties of both clusters are consistent with the high-redshift L-X-T relation measured from X-ray-selected samples at z greater than or equal to 0.5. However, based on the local relations, their X-ray luminosities and temperatures are low for z = 0.5 their measured velocity dispersions (sigma). The clusters are cooler by a factor of 2-9 compared to the local sigma-T relation. We briefly discuss the possible explanations for these results.
View Full Publication open_in_new
Abstract
We present the first detailed X-ray observations of optically selected clusters at high redshift. Two clusters, Cl 1324 + 3011 at z = 0.76 and Cl 1604 + 4304 at z = 0.90, were observed with XMM-Newton. The optical center of each cluster is coincident with an extended X-ray source whose emission is detected out to a radius of similar to0.5 h(70)(-1) Mpc. The emission from each cluster appears reasonably circular, with some indication of asymmetries and more complex morphologies. Similar to other optically selected clusters at redshifts of z greater than or similar to0.4, both clusters are modest X-ray emitters with bolometric luminosities of only L-X(bol) = (1.4-2.0) x 10(44) h(70)(-2) ergs s(-1). We measure gas temperatures of T = 2.88(-0.49)(+0.71) keV for Cl 1324 + 3011 and 2.51(-0.69)(+1.05) keV for Cl 1604 + 4304. The X-ray properties of both clusters are consistent with the high-redshift L-X-T relation measured from X-ray-selected samples at z greater than or equal to 0.5. However, based on the local relations, their X-ray luminosities and temperatures are low for z = 0.5 their measured velocity dispersions (sigma). The clusters are cooler by a factor of 2-9 compared to the local sigma-T relation. We briefly discuss the possible explanations for these results.
View Full Publication open_in_new
Abstract
We present the first detailed X-ray observations of optically selected clusters at high redshift. Two clusters, Cl 1324 + 3011 at z = 0.76 and Cl 1604 + 4304 at z = 0.90, were observed with XMM-Newton. The optical center of each cluster is coincident with an extended X-ray source whose emission is detected out to a radius of similar to0.5 h(70)(-1) Mpc. The emission from each cluster appears reasonably circular, with some indication of asymmetries and more complex morphologies. Similar to other optically selected clusters at redshifts of z greater than or similar to0.4, both clusters are modest X-ray emitters with bolometric luminosities of only L-X(bol) = (1.4-2.0) x 10(44) h(70)(-2) ergs s(-1). We measure gas temperatures of T = 2.88(-0.49)(+0.71) keV for Cl 1324 + 3011 and 2.51(-0.69)(+1.05) keV for Cl 1604 + 4304. The X-ray properties of both clusters are consistent with the high-redshift L-X-T relation measured from X-ray-selected samples at z greater than or equal to 0.5. However, based on the local relations, their X-ray luminosities and temperatures are low for z = 0.5 their measured velocity dispersions (sigma). The clusters are cooler by a factor of 2-9 compared to the local sigma-T relation. We briefly discuss the possible explanations for these results.
View Full Publication open_in_new
Abstract
We present the first detailed X-ray observations of optically selected clusters at high redshift. Two clusters, Cl 1324 + 3011 at z = 0.76 and Cl 1604 + 4304 at z = 0.90, were observed with XMM-Newton. The optical center of each cluster is coincident with an extended X-ray source whose emission is detected out to a radius of similar to0.5 h(70)(-1) Mpc. The emission from each cluster appears reasonably circular, with some indication of asymmetries and more complex morphologies. Similar to other optically selected clusters at redshifts of z greater than or similar to0.4, both clusters are modest X-ray emitters with bolometric luminosities of only L-X(bol) = (1.4-2.0) x 10(44) h(70)(-2) ergs s(-1). We measure gas temperatures of T = 2.88(-0.49)(+0.71) keV for Cl 1324 + 3011 and 2.51(-0.69)(+1.05) keV for Cl 1604 + 4304. The X-ray properties of both clusters are consistent with the high-redshift L-X-T relation measured from X-ray-selected samples at z greater than or equal to 0.5. However, based on the local relations, their X-ray luminosities and temperatures are low for z = 0.5 their measured velocity dispersions (sigma). The clusters are cooler by a factor of 2-9 compared to the local sigma-T relation. We briefly discuss the possible explanations for these results.
View Full Publication open_in_new
Abstract
We present results from an analysis of FUSE spectroscopy of the z(em) = 0.57 quasar PKS 0405 - 123. We focus on the intervening metal-line systems identified along the sight line and investigate their ionization mechanism, ionization state, and chemical abundances. Including Hubble Space Telescope STIS spectroscopy, we survey the entire sight line and identify six O VI absorbers to a 3 sigma equivalent width (EW) limit of 60 mAngstrom. This implies an incidence dN/dz = 16(-6)(+9) consistent with previous O VI studies. In half of the O VI systems we report positive detections of C III, suggesting that the gas is predominantly photoionized, has multiple ionization phases, or is in a nonequilibrium state. This contrasts with the general description of the warm-hot intergalactic medium (WHIM) as described by numerical simulations in which the gas is predominantly in collisional ionization equilibrium. An appreciable fraction of O vi absorbers may therefore have a different origin. We have also searched the sight line for the Ne VIII doublet (a better probe of the WHIM at T > 10(6) K) over the redshift range 0.2 < z < z(em). We report no positive detections to an EW limit of 80 mAngstrom, giving dN/dz < 40 at 95% c. l. The photoionized metal-line systems exhibit a correlation between the ionization parameter (U = Phi/cn(H), with Phi the flux of hydrogen ionizing photons) and H I column density for N(H I) = 10(14)-10(16) cm(-2). Both the slope and normalization of this correlation match the prediction inferred from the results of Dave and Tripp for the low-z Ly alpha forest. In turn, the data show a tentative, unexpected result: five out of the six photoionized metal-line systems show a total hydrogen column density within a factor of 2 of 10(18.7) cm(-2). Finally, the median metallicity [M/H] of twelve z similar to 0.3 absorbers with N(H I)> 10(14) cm(-2) is [M/H] > - 1.5, with large scatter. This significantly exceeds the median metallicity of C IV and O VI systems at z similar to 3 and indicates enrichment of the intergalactic medium over the past approximate to 10 Gyr.
View Full Publication open_in_new
Abstract
We present results from an analysis of FUSE spectroscopy of the z(em) = 0.57 quasar PKS 0405 - 123. We focus on the intervening metal-line systems identified along the sight line and investigate their ionization mechanism, ionization state, and chemical abundances. Including Hubble Space Telescope STIS spectroscopy, we survey the entire sight line and identify six O VI absorbers to a 3 sigma equivalent width (EW) limit of 60 mAngstrom. This implies an incidence dN/dz = 16(-6)(+9) consistent with previous O VI studies. In half of the O VI systems we report positive detections of C III, suggesting that the gas is predominantly photoionized, has multiple ionization phases, or is in a nonequilibrium state. This contrasts with the general description of the warm-hot intergalactic medium (WHIM) as described by numerical simulations in which the gas is predominantly in collisional ionization equilibrium. An appreciable fraction of O vi absorbers may therefore have a different origin. We have also searched the sight line for the Ne VIII doublet (a better probe of the WHIM at T > 10(6) K) over the redshift range 0.2 < z < z(em). We report no positive detections to an EW limit of 80 mAngstrom, giving dN/dz < 40 at 95% c. l. The photoionized metal-line systems exhibit a correlation between the ionization parameter (U = Phi/cn(H), with Phi the flux of hydrogen ionizing photons) and H I column density for N(H I) = 10(14)-10(16) cm(-2). Both the slope and normalization of this correlation match the prediction inferred from the results of Dave and Tripp for the low-z Ly alpha forest. In turn, the data show a tentative, unexpected result: five out of the six photoionized metal-line systems show a total hydrogen column density within a factor of 2 of 10(18.7) cm(-2). Finally, the median metallicity [M/H] of twelve z similar to 0.3 absorbers with N(H I)> 10(14) cm(-2) is [M/H] > - 1.5, with large scatter. This significantly exceeds the median metallicity of C IV and O VI systems at z similar to 3 and indicates enrichment of the intergalactic medium over the past approximate to 10 Gyr.
View Full Publication open_in_new
Abstract
We present results from an analysis of FUSE spectroscopy of the z(em) = 0.57 quasar PKS 0405 - 123. We focus on the intervening metal-line systems identified along the sight line and investigate their ionization mechanism, ionization state, and chemical abundances. Including Hubble Space Telescope STIS spectroscopy, we survey the entire sight line and identify six O VI absorbers to a 3 sigma equivalent width (EW) limit of 60 mAngstrom. This implies an incidence dN/dz = 16(-6)(+9) consistent with previous O VI studies. In half of the O VI systems we report positive detections of C III, suggesting that the gas is predominantly photoionized, has multiple ionization phases, or is in a nonequilibrium state. This contrasts with the general description of the warm-hot intergalactic medium (WHIM) as described by numerical simulations in which the gas is predominantly in collisional ionization equilibrium. An appreciable fraction of O vi absorbers may therefore have a different origin. We have also searched the sight line for the Ne VIII doublet (a better probe of the WHIM at T > 10(6) K) over the redshift range 0.2 < z < z(em). We report no positive detections to an EW limit of 80 mAngstrom, giving dN/dz < 40 at 95% c. l. The photoionized metal-line systems exhibit a correlation between the ionization parameter (U = Phi/cn(H), with Phi the flux of hydrogen ionizing photons) and H I column density for N(H I) = 10(14)-10(16) cm(-2). Both the slope and normalization of this correlation match the prediction inferred from the results of Dave and Tripp for the low-z Ly alpha forest. In turn, the data show a tentative, unexpected result: five out of the six photoionized metal-line systems show a total hydrogen column density within a factor of 2 of 10(18.7) cm(-2). Finally, the median metallicity [M/H] of twelve z similar to 0.3 absorbers with N(H I)> 10(14) cm(-2) is [M/H] > - 1.5, with large scatter. This significantly exceeds the median metallicity of C IV and O VI systems at z similar to 3 and indicates enrichment of the intergalactic medium over the past approximate to 10 Gyr.
View Full Publication open_in_new
Abstract
Deviations of galaxy groups from cluster scaling relations can be understood in terms of an excess of entropy in groups. The main effect of this excess is to reduce the density and thus the luminosity of the intragroup gas. Given this, groups should also show a steep relationship between X-ray luminosity and velocity dispersion. However, previous work suggests that this is not the case, with many measuring slopes flatter than the cluster relation. Examining the group L(X)-sigma relation shows that much of the flattening is caused by a small subset of groups that show very high X-ray luminosities for their velocity dispersions (or vice versa). Detailed Chandra study of two such groups shows that earlier ROSAT results were subject to significant (similar to30%-40%) point-source contamination but confirm that a significant hot intergalactic medium is present in these groups, although these are two of the coolest systems in which intergalactic X-ray emission has been detected. Their X-ray properties are shown to be broadly consistent with those of other galaxy groups, although the gas entropy in NGC 1587 is unusually low, and its X-ray luminosity is correspondingly high for its temperature when compared with most groups. This leads us to suggest that the velocity dispersion in these systems has been reduced in some way, and we consider how this might have come about.
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