1212.1451
Isolated ellipticals and their globular cluster systems I:
Washington photometry of NGC 3585 and NGC 5812
Lane, Salinas, Richter
GC systems of isolated elliptical galaxies: may exhibit morphological connections to the evolutionary histories of their hosts. The GC colors and specific frequencies are highly indicative that the host galaxy environment plays a role in shaping its GC system. Subtracting accurate models of each galaxy reveals underlying features: NGC 5812 is interacting with a dwarf companion galaxy. From models, determine surface brightness and color profiles. Both color profiles appear quite flat and with C-R~1.7; discuss apparent youth of 3585.
1212.1452
Simulations of magnetic fields in isolated disk galaxies
Pakmor, Springel
B-fields dynamically important in ISM, ubiquitously observed in diffuse gas in haloes of galaxies and galaxy clusters; but neglected in galaxy formation studies. Extend MHD in moving-mesh code Arepo to cosmological problems which include radiative cooling and formation of stars. Replace divergence cleaning approach with Powell 8-wave scheme, which is more stable. Verify improved accuracy through simulations of MRI in accretion disks. Simulate the formation of isolated disk galaxies similar to MW using idealized IC with and without B-fields. Find: B-field is quickly amplified in initial SB and the differential rotation of the forming disk until it eventually saturates when it becomes comparable to the thermal pressure. The additional pressure component leads to a lower SFR at late times compared to simulations w/o B-fields; induced changes in the spiral arm structures of the gas disk. In addition, observe highly magnetized fountain-like outflows from the disk. These results are robust with numerical resolution and are largely independent of the initial magnetic seed field assumed in IC, as the amplification is rapid and self-regulated. Findings suggest an important influence of B-field on galaxy formation and evolution.
1212.1454
Cosmic vorticity and the origin of halo spins
Libeskind et al
Cosmological structure emerges out of non-rotational flow and the angular momentum of collapsing halos is induced by tidal torques. The growth of halo angular momentum in the linear and quasi-linear phases is associated with a shear, curl-free, flow and it is well described within the linear framework of tidal torque theory (TTT). TTT rendered irrelvant as the halo is virialized: at this stage the flow field around haloes has non-zero vorticity. Examine the importance of the curl of the velocity field (vorticity) in determining halo spin; find a strong alignment between the two. Examine alignment of the vorticity with the principle axes of the shear tensor, find that it tends to be perpendicular to the axis along which material is collapsing fastest (e1). This behavior is independent of halo masses and cosmic web environment. Results agree with previous findings (halo spin perp to e1; spin of simulated haloes and observed galaxies aligned with large-scale structure). Results imply that angular momentum growth proceeds in tow distinct phases: (1) first phase, angular momentum emerges out of shear, curl-free, potential flow, described by TTT. (2) second phase, haloes approach virialization, angular momentum emerges out of a vortical flow and halo spin becomes strongly aligned with vorticity of the ambient flow field.
1212.1455
MAMPOSSt: Modelling anisotropy and mass profiles of observed spherical systems. I. Gaussian 3d velocities
Mamon
Performs a maximum likelihood fit of the distribution of observed tracers in projected phase space; developed and thoroughly tested.Tests show that MAMPOSSt with Gaussin 3d velocities is very competitive with other methods, and can be 1000x faster.
1212.1458
Effect of halo bias and Lyman limit systems on the history of cosmic reionization
Kaurov, Gnedin
Include biasing of reionization sources and additional absorption by LL systems to the analytical reionization model by Furlanetto (2004). Model is consistent with the observed evolution of the galaxy luminosity function at z<8 and with the observed evolution of Lya forest at z<6. Also find that reionization model is consistent with WMAP constraint on Thompson optical depth and with SPT and EDGES constraints on the duration of reionization. Possible to develop physically realistic models of reionization consistent with all existing observational constraints.
1212.1460
Disk stability and neutral hydrogen as a tracer of dark matter
Meurer, Zheng, de Blok
Derive projected surface mass distribution Sigma_M for spherically symmetric mass distributions having an arbitrary rotation curve. For a galaxy with a flat rotation curve and an ISM disk having a constant Toomre stability parameter, the ISM surface mass density Sigma_g as well as Sigma_M both fall off as 1/R. Use published data on a sample of 20 well studied galaxies to show that ISM disks do maintain a constant Q over all radii usually encompassing more than 50% of the HI mass. Power law slope in Sigma_g covers a range of exponents and is well correlated with the slope in the epicyclic frequency. Implies that the ISM disk is responding to the potential, and hence that secular evolution is important for setting the structure of ISM disks. Show that the gas to total mass ratio should be anti-correlated with the maximum rotational velocity, and that the sample falls on the expected relationship. A very steep fall off in Sigma_g is required at the outermost radii to keep the mass and angular momentum content finite for typical rotation curve shapes, and is observed. The observation that HI traces dark matter over a significant range of radii in galaxies is thus due to the disks stabilising themselves in a normal dark matter dominated potential. This explanation is consistent with the CDM paradigm.
1212.1463
Cosmological evolution of galaxies
Shlosman
[winter school lecture notes]: review the subject of cosmological evolution of galaxies, including different aspects of growth in disk galaxies, by focussing on the angular momentum problem, mergers, and their by-products. Discuss: alternative to merger-driven growth -- cold accretion and related issues. Possible feedback mechanisms and their role in galaxy evolution. Special attention is paid to high-redhsift galaxies and their properties. Discuss a number of processes, gas- and stellar-dynamical, within the central kiloparsec of disk galaxies, and their effect on the large spatial scales, as well as on the formation and fuelling of the seed black holes in galactic centers at high z.
1212.1576
Cosmology with large redshift surveys
Sodre
Galaxy z-surveys: tool to address DE nature & DM properties. Others: study of small bodies in the solar system; tidal streams in the MW halo, galaxy formation and evolution. Discuss what a z survey is and how it can be used to attack astrophysical and cosmological problems. Finish with a brief description of a new survey (JPAS): 56 filters of 8k sq deg. JPAS photometric system: provide accurate photometric z; deliver a low-resolution spectrum at each pixel on the sky, allowing for the first time an almost all-sky IFU science.
1212.1597
The extended ROSAT-ESO flux limited X-ray galaxy cluster survey (REFLEX II) III. construction of the first flux-limited supercluster sample
Chon, Boehringer, Nowak
From 919 X-ray selected galaxy clusters, construct a supercluster catalog using FoF with a linking length depending on the local cluster density. 164 superclusters at z<=0.4. Study the properties of different catalogues such as the distribution of the z, extent and multiplicity by varying the choice of parameters. In addition to the main catalogue, compile a large volume-limited cluster sample to investigate the statistics of the superclusters. Compare the X-ray luminosity function for the clusters in superclusters with that for the field clusters with the flux- and volume-limited catalogues. Results mildly support the theoretical suggestion of a top-heavy X-ray luminosity function of galaxy clusters in regions of high cluster density.
1212.1613
The baryon budget on the galaxy group/cluster boundary
Sanderson, O'Sullivan, ... Gonzalez, .. Zabludoff, Zaritzky, et al
Study of the hot gas and stellar content of 5 optically-selected poor galaxy clusters, including a full accounting of the contirbution from ICL and a combined hot gas and hydrostatic X-ray mass analysis with XMM observations. Find weighted mean stellar (+ICL), gas, and total baryon mass fractions within r500 of 0.026 (star), 0.070 (gas), 0.096 (total baryon), respectively, at a corresponding wighted mean M500 of 1e14 Msun. Even when accounting for the ICL stars, 4/5 clusters show evidence fo a substantial baryon deficit within r500, with baryon fraction (f_bary) between 50 to 59% of the universal mean level (Omega_b / Omega_m); the remaining cluster having f_bary=75 %. For the 3 clusters where the hot halo can be traced to r500, find no evidence for a steepening of the gas density profile in the outskirts with respect to a power law, as seen in more massive clusters. Find that in all cases, the X-ray mass measurements are larger than those originally published on the basis of the galaxy velocity dispersion (sigma) and an assumed sigma-M500 relation, by a factor of 1.7-5.7. Despite these increased masses, the stellar fractions (in the range 0.016-0.034, within r500) remain consistent with the trend with mass published by Gonzalez, Zaritsky & Zabludoff (2007), from which this sample is drawn.
1212.1619
The small scale dynamo and the amplification of magnetic fields in massive primordial haloes
Latif, Schleicher, Schmidt, Niemeyer
No clear prediction for the initial B-field strength from present standard model of cosmology, but efficient dynamo action may compensate for initially weak seed fields via rapid amplification. In particular, the small-scale dynamo is expected to exponentially amplify any weak B-field in the presence of turbulence. Explore whether this scenario is viable using cosmological MHD simulations modeling the formation of the first galaxies, which are expected to form in so-called atomic cooling haloes with virial temperature T_vir>1e4K. As previous calculations have shown that a high Jeans resolution is needed to resolve turbulent structures and dynamo effects, calculations employ resolutions of up to 128 cells per Jeans length. The presence of the dynamo can be clearly confirmed for resolutions of at least 64 cells per Jeans length, while saturation occurs at approximate equipartition with turbulent energy. As a result of the large Reynolds numbers in primoridal galaxies, expect saturation to occur at early stages, implying B-field strengths of ~0.1 uG at densities of 1e4/cm^3.
1212.1624
Imaging on PAPER: Centaurus A at 148 MHz
Stefan, .. .Aguirre, ... Parsons, ... Pober, ... et al
Observations taken with Donald C. Backer PAPER of Centaurus A field of 120 to 180 Mhz. Dynamic range of 3000; rms of 0.5 Jy/beam. Spectral index map of Cen A is produced across the full band. The spectral index distribution is qualitatively consistent with electron reacceleration in regions of excess turbulence in the radio lobes, as previously identified morphologically. Hence, there appears to be an association of 'severe weather' in radio lobes with energy input into the relativistic electron population. Perform a detailed comparison of the large scale radio and X-ray emission from the ROSAT All Sky Survey. While the ROSAT field has significant gradients and structures on 10 deg scales possibly unrelated to Cen A, two interesting correlations are seen between the radio and X-ray emission. First is an apparent 'cavity' generated by the northern radio lobe on a scale of 5 deg, possibly indicating excavation of thermal gas by the expanding radio source. Second is a correlation between radio and X-ray 'hot spots' at the end of the southern lobe, some 200 kpc from the nucleus. This likely arises from Inverse Compton scattering of the CMB by the relativistic electrons also responsible for the radio synchrotron emission. The B-fields derived from the (possible) IC and radio emission are of similar magnitude as the minimum pressure fields, ~1 uG.
1212.1683
Extragalactic background light from hierarchical galaxy formation: gamma-ray attenuation up to the epoch of cosmic reionization and the first stars
Inoue, .. Totani et al
Model of the extragalactic background light (EBL) and corresponding gamma-gamma opacity for intergalactic gamma-ray absorption from z=0 up to z=10, based on SAM that reproduces key observed properties of galaxies at various redshifts. Include potential contribution from Pop III stars in a simplified way; the model is broadly consistent with available data concerning cosmic reionization, particularly the Thomson scattering optical depth constraints from WMAP. In coparison with previous EBL studies up to z~3-5, predicted gamma-gamma opacity is in general agreement for observed gamma-ray energy below 400/(1+z) GeV, whereas it is a factor of 2 lower above this energy because of a correspondingly lower cosmic SFR, even though the observed UV luminosity is well reproduced by virtue of improved treatment of dust obscuration and direct estimation of SFR. The horizon energy at which the gamma-ray opacity is unity does not evolve strongly beyond z~4 and approaches ~20 GeV. The contribution of Pop III stars is a minor fraction of the EBL at z=0, and is also difficult to distinguish through gamma-ray absorption in high-z objects, even at the highest levels allowed by the WMAP constraints. Nevertheless, the attenuation due to Pop II stars should be observable in high-z gamma-ray sources by telescopes such as Fermi or CTA and provide a valuable probe of the evolving EBL in the rest-frame UV.
Cosmic vorticity and the origin of halo spins
Libeskind et al
Cosmological structure emerges out of non-rotational flow and the angular momentum of collapsing halos is induced by tidal torques. The growth of halo angular momentum in the linear and quasi-linear phases is associated with a shear, curl-free, flow and it is well described within the linear framework of tidal torque theory (TTT). TTT rendered irrelvant as the halo is virialized: at this stage the flow field around haloes has non-zero vorticity. Examine the importance of the curl of the velocity field (vorticity) in determining halo spin; find a strong alignment between the two. Examine alignment of the vorticity with the principle axes of the shear tensor, find that it tends to be perpendicular to the axis along which material is collapsing fastest (e1). This behavior is independent of halo masses and cosmic web environment. Results agree with previous findings (halo spin perp to e1; spin of simulated haloes and observed galaxies aligned with large-scale structure). Results imply that angular momentum growth proceeds in tow distinct phases: (1) first phase, angular momentum emerges out of shear, curl-free, potential flow, described by TTT. (2) second phase, haloes approach virialization, angular momentum emerges out of a vortical flow and halo spin becomes strongly aligned with vorticity of the ambient flow field.
1212.1455
MAMPOSSt: Modelling anisotropy and mass profiles of observed spherical systems. I. Gaussian 3d velocities
Mamon
Performs a maximum likelihood fit of the distribution of observed tracers in projected phase space; developed and thoroughly tested.Tests show that MAMPOSSt with Gaussin 3d velocities is very competitive with other methods, and can be 1000x faster.
1212.1458
Effect of halo bias and Lyman limit systems on the history of cosmic reionization
Kaurov, Gnedin
Include biasing of reionization sources and additional absorption by LL systems to the analytical reionization model by Furlanetto (2004). Model is consistent with the observed evolution of the galaxy luminosity function at z<8 and with the observed evolution of Lya forest at z<6. Also find that reionization model is consistent with WMAP constraint on Thompson optical depth and with SPT and EDGES constraints on the duration of reionization. Possible to develop physically realistic models of reionization consistent with all existing observational constraints.
1212.1460
Disk stability and neutral hydrogen as a tracer of dark matter
Meurer, Zheng, de Blok
Derive projected surface mass distribution Sigma_M for spherically symmetric mass distributions having an arbitrary rotation curve. For a galaxy with a flat rotation curve and an ISM disk having a constant Toomre stability parameter, the ISM surface mass density Sigma_g as well as Sigma_M both fall off as 1/R. Use published data on a sample of 20 well studied galaxies to show that ISM disks do maintain a constant Q over all radii usually encompassing more than 50% of the HI mass. Power law slope in Sigma_g covers a range of exponents and is well correlated with the slope in the epicyclic frequency. Implies that the ISM disk is responding to the potential, and hence that secular evolution is important for setting the structure of ISM disks. Show that the gas to total mass ratio should be anti-correlated with the maximum rotational velocity, and that the sample falls on the expected relationship. A very steep fall off in Sigma_g is required at the outermost radii to keep the mass and angular momentum content finite for typical rotation curve shapes, and is observed. The observation that HI traces dark matter over a significant range of radii in galaxies is thus due to the disks stabilising themselves in a normal dark matter dominated potential. This explanation is consistent with the CDM paradigm.
1212.1463
Cosmological evolution of galaxies
Shlosman
[winter school lecture notes]: review the subject of cosmological evolution of galaxies, including different aspects of growth in disk galaxies, by focussing on the angular momentum problem, mergers, and their by-products. Discuss: alternative to merger-driven growth -- cold accretion and related issues. Possible feedback mechanisms and their role in galaxy evolution. Special attention is paid to high-redhsift galaxies and their properties. Discuss a number of processes, gas- and stellar-dynamical, within the central kiloparsec of disk galaxies, and their effect on the large spatial scales, as well as on the formation and fuelling of the seed black holes in galactic centers at high z.
1212.1576
Cosmology with large redshift surveys
Sodre
Galaxy z-surveys: tool to address DE nature & DM properties. Others: study of small bodies in the solar system; tidal streams in the MW halo, galaxy formation and evolution. Discuss what a z survey is and how it can be used to attack astrophysical and cosmological problems. Finish with a brief description of a new survey (JPAS): 56 filters of 8k sq deg. JPAS photometric system: provide accurate photometric z; deliver a low-resolution spectrum at each pixel on the sky, allowing for the first time an almost all-sky IFU science.
1212.1597
The extended ROSAT-ESO flux limited X-ray galaxy cluster survey (REFLEX II) III. construction of the first flux-limited supercluster sample
Chon, Boehringer, Nowak
From 919 X-ray selected galaxy clusters, construct a supercluster catalog using FoF with a linking length depending on the local cluster density. 164 superclusters at z<=0.4. Study the properties of different catalogues such as the distribution of the z, extent and multiplicity by varying the choice of parameters. In addition to the main catalogue, compile a large volume-limited cluster sample to investigate the statistics of the superclusters. Compare the X-ray luminosity function for the clusters in superclusters with that for the field clusters with the flux- and volume-limited catalogues. Results mildly support the theoretical suggestion of a top-heavy X-ray luminosity function of galaxy clusters in regions of high cluster density.
1212.1613
The baryon budget on the galaxy group/cluster boundary
Sanderson, O'Sullivan, ... Gonzalez, .. Zabludoff, Zaritzky, et al
Study of the hot gas and stellar content of 5 optically-selected poor galaxy clusters, including a full accounting of the contirbution from ICL and a combined hot gas and hydrostatic X-ray mass analysis with XMM observations. Find weighted mean stellar (+ICL), gas, and total baryon mass fractions within r500 of 0.026 (star), 0.070 (gas), 0.096 (total baryon), respectively, at a corresponding wighted mean M500 of 1e14 Msun. Even when accounting for the ICL stars, 4/5 clusters show evidence fo a substantial baryon deficit within r500, with baryon fraction (f_bary) between 50 to 59% of the universal mean level (Omega_b / Omega_m); the remaining cluster having f_bary=75 %. For the 3 clusters where the hot halo can be traced to r500, find no evidence for a steepening of the gas density profile in the outskirts with respect to a power law, as seen in more massive clusters. Find that in all cases, the X-ray mass measurements are larger than those originally published on the basis of the galaxy velocity dispersion (sigma) and an assumed sigma-M500 relation, by a factor of 1.7-5.7. Despite these increased masses, the stellar fractions (in the range 0.016-0.034, within r500) remain consistent with the trend with mass published by Gonzalez, Zaritsky & Zabludoff (2007), from which this sample is drawn.
1212.1619
The small scale dynamo and the amplification of magnetic fields in massive primordial haloes
Latif, Schleicher, Schmidt, Niemeyer
No clear prediction for the initial B-field strength from present standard model of cosmology, but efficient dynamo action may compensate for initially weak seed fields via rapid amplification. In particular, the small-scale dynamo is expected to exponentially amplify any weak B-field in the presence of turbulence. Explore whether this scenario is viable using cosmological MHD simulations modeling the formation of the first galaxies, which are expected to form in so-called atomic cooling haloes with virial temperature T_vir>1e4K. As previous calculations have shown that a high Jeans resolution is needed to resolve turbulent structures and dynamo effects, calculations employ resolutions of up to 128 cells per Jeans length. The presence of the dynamo can be clearly confirmed for resolutions of at least 64 cells per Jeans length, while saturation occurs at approximate equipartition with turbulent energy. As a result of the large Reynolds numbers in primoridal galaxies, expect saturation to occur at early stages, implying B-field strengths of ~0.1 uG at densities of 1e4/cm^3.
1212.1624
Imaging on PAPER: Centaurus A at 148 MHz
Stefan, .. .Aguirre, ... Parsons, ... Pober, ... et al
Observations taken with Donald C. Backer PAPER of Centaurus A field of 120 to 180 Mhz. Dynamic range of 3000; rms of 0.5 Jy/beam. Spectral index map of Cen A is produced across the full band. The spectral index distribution is qualitatively consistent with electron reacceleration in regions of excess turbulence in the radio lobes, as previously identified morphologically. Hence, there appears to be an association of 'severe weather' in radio lobes with energy input into the relativistic electron population. Perform a detailed comparison of the large scale radio and X-ray emission from the ROSAT All Sky Survey. While the ROSAT field has significant gradients and structures on 10 deg scales possibly unrelated to Cen A, two interesting correlations are seen between the radio and X-ray emission. First is an apparent 'cavity' generated by the northern radio lobe on a scale of 5 deg, possibly indicating excavation of thermal gas by the expanding radio source. Second is a correlation between radio and X-ray 'hot spots' at the end of the southern lobe, some 200 kpc from the nucleus. This likely arises from Inverse Compton scattering of the CMB by the relativistic electrons also responsible for the radio synchrotron emission. The B-fields derived from the (possible) IC and radio emission are of similar magnitude as the minimum pressure fields, ~1 uG.
1212.1683
Extragalactic background light from hierarchical galaxy formation: gamma-ray attenuation up to the epoch of cosmic reionization and the first stars
Inoue, .. Totani et al
Model of the extragalactic background light (EBL) and corresponding gamma-gamma opacity for intergalactic gamma-ray absorption from z=0 up to z=10, based on SAM that reproduces key observed properties of galaxies at various redshifts. Include potential contribution from Pop III stars in a simplified way; the model is broadly consistent with available data concerning cosmic reionization, particularly the Thomson scattering optical depth constraints from WMAP. In coparison with previous EBL studies up to z~3-5, predicted gamma-gamma opacity is in general agreement for observed gamma-ray energy below 400/(1+z) GeV, whereas it is a factor of 2 lower above this energy because of a correspondingly lower cosmic SFR, even though the observed UV luminosity is well reproduced by virtue of improved treatment of dust obscuration and direct estimation of SFR. The horizon energy at which the gamma-ray opacity is unity does not evolve strongly beyond z~4 and approaches ~20 GeV. The contribution of Pop III stars is a minor fraction of the EBL at z=0, and is also difficult to distinguish through gamma-ray absorption in high-z objects, even at the highest levels allowed by the WMAP constraints. Nevertheless, the attenuation due to Pop II stars should be observable in high-z gamma-ray sources by telescopes such as Fermi or CTA and provide a valuable probe of the evolving EBL in the rest-frame UV.
No comments:
Post a Comment