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Register a new userThe temperature of hot gas halos of early-type galaxies
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Silvia Pellegrini dr.
Publication date
2011
fields
Physics
and research's language is
English
Authors
S. Pellegrini
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Recently, the temperature T and luminosity L_X of the hot gas halos of early type galaxies have been derived with unprecedented accuracy from Chandra data, for 30 galaxies covering a wider range of galactic luminosity (and central velocity dispersion sigma_c) than before. This work investigates the origin of the observed temperatures, by examining the relationship between them and the galaxy structure, the gas heating due to Type Ia supernovae (SNIas) and the gravitational potential, and the dynamical status of the gas flow. In galaxies with sigma_c<200 km/s, the Ts are close to a fiducial average temperature for the gas when in outflow; at 200<sigma_c (km/s)<250, the Ts are generally lower than this, and unrelated with sigma_c, which requires a more complex gas flow status; at larger sigma_c, the Ts may increase as sigma_c^2, as expected for infall heating, though heating from SNIas, independent of sigma_c, should be dominant. All observed Ts are larger than the virial temperature, by up to ~0.5 keV. This additional heating can be provided in the X-ray brightest galaxies by SNIas and infall heating, with a SNIas energy input even lower than in standard assumptions; in the X-ray fainter ones it can be provided by SNIas, whose energy input would be required close to the full standard value at the largest sigma_c. This same energy input, though, would produce temperatures larger than observed at low sigma_c, if entirely thermalized. The values of the observed Ts increase from outflows to inflows; the gas is relatively hotter in outflows, though, if the Ts are rescaled by the virial temperature. For 200<sigma_c(km/s)<250, lower L_X values tend to correspond to lower Ts, which deserves further investigation.
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Using the data products of the Chandra Galaxy Atlas (Kim et al. 2019a), we have investigated the radial profiles of the hot gas temperature in 60 early type galaxies. Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at RMAX = 35 +/- 25 kpc (or ~0.04 RVIR) and declines both inward and outward. The temperature dips (or breaks) at RMIN (or RBREAK) = 3 - 5 kpc (or ~0.006 RVIR). The mean slope between RMIN (RBREAK) and RMAX is 0.3 +/- 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72% (possibly up to 82%) of our ETG sample. The remaining ETGs (18%) with irregular or monotonically declining profiles do not fit the universal profile and require another explanation. The temperature gradient inside RMIN (RBREAK) varies widely, indicating different degrees of additional heating at small radii. Investigating the nature of the hot core (HC with a negative gradient inside RMIN), we find that HC is most clearly visible in small galaxies. Searching for potential clues associated with stellar, AGN feedback, and gravitational heating, we find that HC may be related to recent star formation. But we see no clear evidence that AGN feedback and gravitational heating play any significant role for HC.
A recent determination of the relationships between the X-ray luminosity of the ISM (Lx) and the stellar and total mass, for a sample of nearby early-type galaxies (ETGs), is used to investigate the origin of the hot gas, via a comparison with the results of hydrodynamical simulations of the ISM evolution for a large set of isolated ETGs. After the epoch of major galaxy formation (after z~2), the ISM is replenished by stellar mass losses and SN ejecta, at the rate predicted by stellar evolution, and is depleted by star formation; it is heated by the thermalization of stellar motions, SNe explosions and the mechanical (from winds) and radiative AGN feedback. The models agree well with the observed relations, even for the largely different Lx values at the same mass, thanks to the sensitivity of the gas flow to many galaxy properties; this holds for models including AGN feedback, and those without. Therefore, the mass input from the stellar population is able to account for a major part of the observed Lx; and AGN feedback, while very important to maintain massive ETGs in a time-averaged quasi-steady state, keeping low star formation and the black hole mass, does not dramatically alter the gas content originating in stellar recycled material. These conclusions are based on theoretical predictions for the stellar population contributions in mass and energy, and on a self-consistent modeling of AGN feedback.
For early-type galaxies, the ability to sustain a corona of hot, X-ray emitting gas could have played a key role in quenching their star-formation history. Yet, it is still unclear what drives the precise amount of hot gas around these galaxies. By combining photometric and spectroscopic measurements for the early-type galaxies observed during the Atlas3D integral-field survey with measurements of their X-ray luminosity based on X-ray data of both low and high spatial resolution we conclude that the hot-gas content of early-type galaxies can depend on their dynamical structure. Specifically, whereas slow rotators generally have X-ray halos with luminosity L_X,gas and temperature T values that are in line with what is expected if the hot-gas emission is sustained by the thermalisaton of the kinetic energy carried by the stellar-mass loss material, fast rotators tend to display L_X,gas values that fall consistently below the prediction of this model, with similar T values that do not scale with the stellar kinetic energy as observed in the case of slow rotators. Considering that fast rotators are likely to be intrinsically flatter than slow rotators, and that the few L_X,gas-deficient slow rotators also happen to be relatively flat, the observed L_X,gas deficiency in these objects would support the hypothesis whereby flatter galaxies have a harder time in retaining their hot gas. We discuss the implications that a different hot-gas content could have on the fate of both acquired and internally-produced gaseous material, considering in particular how the L_X,gas deficiency of fast rotators would make them more capable to recycle the stellar-mass loss material into new stars than slow rotators. This is consistent with the finding that molecular gas and young stars are detected only in fast rotators in the Atlas3D sample, and that fast rotators tend to dustier than slow rotators. [Abridged]
Optically-similar early-type galaxies are observed to have a large and poorly understood range in the amount of hot, X-ray-emitting gas they contain.To investigate the origin of this diversity, we studied the hot gas properties of all 42 early-type galaxies in the multiwavelength ATLAS$^{rm 3D}$ survey that have sufficiently deep {sl Chandra} X-ray observations. We related their hot gas properties to a number of internal and external physical quantities. To characterize the amount of hot gas relative to the stellar light, we use the ratio of the gaseous X-ray luminosity to the stellar $K$-band luminosity, $L_{X_{rm gas}}/L_K$; we also use the deviations of $L_{X_{rm gas}}$ from the best-fit $L_{X_{rm gas}}$--$L_K$ relation (denoted $Delta L_{X_{rm gas}}$). We quantitatively confirm previous suggestions that various effects conspire to produce the large scatter in the observed $L_X/L_K$ relation. In particular, we find that the deviations $Delta L_{X_{rm gas}}$ are most strongly positively correlated with the (low rates of) star formation and the hot gas temperatures in the sample galaxies. This suggests that mild stellar feedback may energize the gas without pushing it out of the host galaxies. We also find that galaxies in high galaxy density environments tend to be massive slow-rotators, while galaxies in low galaxy density environments tend to be low mass, fast-rotators. Moreover, cold gas in clusters and fields may have different origins. The star formation rate increases with cold gas mass for field galaxies but it appears to be uncorrelated with cold gas for cluster galaxies.
We present results of optical broad-band and narrow-band Halpha observations of a sample of forty nearby early-type galaxies. The majority of sample galaxies are known to have dust in various forms viz. dust lanes, nuclear dust and patchy/filamentary dust. A detailed study of dust was performed for 12 galaxies with prominent dust features. The extinction curves for these galaxies run parallel to the Galactic extinction curve, implying that the properties of dust in these galaxies are similar to those of the Milky-Way. The ratio of total to selective extinction (Rv) varies between 2.1 and 3.8, with an average of 2.9 +/- 0.2, fairly close to its canonical value of 3.1 for our Galaxy. The average relative grain size <a>/a_Gal of dust particles in these galaxies turns out to be 1.01 +/- 0.2, while dust mass estimated using optical extinction lies in the range 10^2 to 10^4 M(sun) . The Halpha emission was detected in 23 out of 29 galaxies imaged through narrow- band filters with the Halpha luminosities in the range 10^38 - 10^41 erg s^-1. The mass of the ionized gas is in the range 10^3-10^5 M(sun). The morphology and extent of ionized gas is found similar to those of dust, indicating possible coexistence of dust and ionized gas in these galaxies. The absence of any apparent correlation between blue luminosity and normalized IRAS dust mass is suggestive of merger related origin of dust and gas in these galaxies.
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