We present new ALMA CO(2-1) observations of two well-studied group-centered elliptical galaxies: NGC 4636 and NGC 5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the ...central galaxy in the NGC 5044 group. We find evidence that molecular gas is a common presence in bright group-centered galaxies (BGG). CO line widths are broader than Galactic molecular clouds, and using the reference Milky Way XCO, the total molecular mass ranges from 2.6 × 105 M in NGC 4636 to 6.1 × 107 M in NGC 5044. Complementary observations using the ALMA Compact Array do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps, suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm ( )/hot (≥106) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistent with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.
We measure several properties of the reionization process and the corresponding low-frequency 21 cm signal associated with the neutral hydrogen distribution, using a large volume, high-resolution ...simulation of cosmic reionization. The brightness temperature of the 21 cm signal is derived by postprocessing this numerical simulation with a semianalytical prescription. Our study extends to high redshifts where, in addition to collisional coupling, our postprocessed simulations take into account the inhomogeneities in the heating of the neutral gas by X-rays and the effect of an inhomogeneous image radiation field. Unlike the well-studied case in which spin temperature is assumed to be significantly greater than the temperature of the cosmic microwave background due to uniform heating of the gas by X- rays, spatial fluctuations in both the image radiation field and X-ray intensity affect predictions related to the brightness temperature at image, during the early stages of reionization and gas heating. The statistics of the 21 cm signal from our simulation are then compared to existing analytical models in the literature, and we find that these analytical models provide a reasonably accurate description of the 21 cm power spectrum at image. Such an agreement is useful, since analytical models are better suited to quickly explore the full astrophysical and cosmological parameter space relevant for future 21 cm surveys. We find, nevertheless, nonnegligible differences that can be attributed to differences in the inhomogeneous X-ray heating and image coupling at image, and, with upcoming interferometric data, these differences in return can provide a way to better understand the astrophysical processes during reionization.
Recent work suggests that Type Ia supernovae (SNe) are composed of two distinct populations: prompt and delayed. By explicitly incorporating properties of host galaxies, it may be possible to target ...and eliminate systematic differences between these two putative populations. However, any resulting post-calibration shift in luminosity between the components will cause a redshift-dependent systematic shift in the Hubble diagram. Utilizing an existing sample of 192 SNe Ia, we find that the average luminosity difference between prompt and delayed SNe is constrained to be%. If the absolute difference between the two populations is 0.025 mag, and this is ignored when fitting for cosmological parameters, then the dark energy equation of state (EOS) determined from a sample of 2300 SNe Ia is biased at image1 capital sigma . By incorporating the possibility of a two-population systematic, this bias can be eliminated. However, assuming no prior on the strength of the two-population effect, the uncertainty in the best-fit EOS is increased by a factor of 2.5, when compared to the equivalent sample with no underlying two-population systematic. To avoid introducing a bias in the EOS parameters, or significantly degrading the measurement accuracy, it is necessary to control the postcalibration luminosity difference between prompt and delayed SN populations to better than 0.025 mag.
We introduce a fast Markov Chain Monte Carlo (MCMC) exploration of the astrophysical parameter space using a modified version of the publicly available code Code Investigating GALaxy Emission ...(CIGALE). The original CIGALE builds a grid of theoretical spectral energy distribution (SED) models and fits to photometric fluxes from ultraviolet to infrared to put constraints on parameters related to both formation and evolution of galaxies. Such a grid-based method can lead to a long and challenging parameter extraction since the computation time increases exponentially with the number of parameters considered and results can be dependent on the density of sampling points, which must be chosen in advance for each parameter. MCMC methods, on the other hand, scale approximately linearly with the number of parameters, allowing a faster and more accurate exploration of the parameter space by using a smaller number of efficiently chosen samples. We test our MCMC version of the code CIGALE (called CIGALEMC) with simulated data. After checking the ability of the code to retrieve the input parameters used to build the mock sample, we fit theoretical SEDs to real data from the well-known and -studied Spitzer Infrared Nearby Galaxy Survey sample. We discuss constraints on the parameters and show the advantages of our MCMC sampling method in terms of accuracy of the results and optimization of CPU time.
The Hubble morphological sequence from early to late galaxies corresponds to an increasing rate of specific star formation. The Hubble sequence also follows a banana-shaped correlation between 24 and ...70 mu m luminosities, both normalized with the K-band luminosity. We show that this correlation is significantly tightened if galaxies with central active galactic nucleus (AGN) emission are removed, but the cosmic scatter of elliptical galaxies in both 24 and 70 mu m luminosities remains significant along the correlation. We find that the 24 mu m variation among ellipticals correlates with stellar metallicity, reflecting emission from hot dust in winds from asymptotic giant branch stars of varying metallicity. Elliptical galaxies evidently undergo large transient excursions in the banana plot in times comparable to the sputtering time or AGN duty cycle, 10 Myr. Normally regarded as passive, elliptical galaxies are the most active galaxies in the IR color-color correlation.
Dusty, star-forming galaxies and active galactic nuclei that contribute to the Integrated background intensity at far-Infrared wavelengths trace the large-scale structure. Below the point-source ...detection limit, correlations in the large-scale structure lead to clustered anisotropies in the unresolved component of the far-infrared background (FIRB). The angular power spectrum of the FIRB anisotropies could be measured in large-area surveys with the Spectral and Photometric Imaging Receiver (SPIRE) on the upcoming Herschel Space Observatory. To study statistical properties of these anisotropies, the confusion from foreground Galactic dust emission needs to be reduced, even in the "cleanest" regions of the sky. The multifrequency coverage of SPIRE allows the foreground dust to be partly separated from the extragalactic background, composed of dusty star-forming galaxies as well as faint normal galaxies. The separation improves for fields with sizes greater than a few hundred square degrees and when combined with Planck data. We show that an area of similar to 400 deg super(2) observed for about 1000 hr with Herschel SPIRE and complemented by Planck provides maximal information on the anisotropy power spectrum. We discuss the scientific studies that can be done with measurements of the unresolved FIRB anisotropies, including a determination of the large-scale bias and the small-scale halo occupation distribution of FIRB sources with fluxes below the point-source detection level.
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