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Register a new userX-raying the Winds of Luminous Active Galaxies
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We briefly describe some recent observational results, mainly at X-ray wavelengths, on the winds of luminous active galactic nuclei (AGNs). These winds likely play a significant role in galaxy feedback. Topics covered include (1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL) and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3) Evidence for relativistic iron K BALs in the X-ray spectra of a few bright quasars. We also mention some key outstanding problems and prospects for future advances; e.g., with the International X-ray Observatory (IXO).
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Theoretical models of wind-driven feedback from Active Galactic Nuclei (AGN) often identify Ultra-fast outflows (UFOs) as being the main cause for generating galaxy-size outflows, possibly the main actors in establishing the so-called AGN-galaxy co-evolution. UFOs are well characterized in local AGN but much less is known in quasars at the cosmic time when SF and AGN activity peaked ($zsimeq1-3$). It is therefore mandatory to search for evidences of UFOs in high-$z$ sources to test the wind-driven AGN feedback models. Here we present a study of Q2237+030, the Einstein Cross, a quadruply-imaged radio-quiet lensed quasar located at $z=1.695$. We performed a systematic and comprehensive temporally and spatially resolved X-ray spectral analysis of all the available Chandra and XMM-Newton data (as of September 2019). We find clear evidence for spectral variability, possibly due to absorption column density (or covering fraction) variability intrinsic to the source. We detect, for the first time in this quasar, a fast X-ray wind outflowing at $v_{rm out}simeq0.1c$ that would be powerful enough ($dot{E}_{rm kin}simeq0.1 L_{rm bol}$) to significantly affect the host galaxy evolution. We report also on the possible presence of an even faster component of the wind ($v_{rm out}sim0.5c$). Given the large sample and long time interval spanned by the analyzed X-ray data, we are able to roughly estimate, for the first time in a high-$z$ quasar, the wind duty cycle as $approx0.46,(0.31)$ at $90%,(95%)$ confidence level. Finally, we also confirm the presence of a Fe K$alpha$ emission line with variable energy, which we discuss in the light of microlensing effects as well as considering our findings on the source.
We present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG), NGC3256. The first, SN2018ec, was discovered using the ESO HAWK-I/GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of $A_V=2.1^{+0.3}_{-0.1}$ mag. The second, AT2018cux, was discovered during the course of follow-up observations of SN2018ec, and is consistent with a sub-luminous Type IIP classification with an $A_V=2.1 pm 0.4$ mag of host extinction. A third CCSN, PSNJ10275082-4354034 in NGC3256, has previously been reported in 2014, and we recovered the source in late time archival HST imaging. Based on template light-curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of $A_V=0.3^{+0.4}_{-0.3}$ mag. We also extend our study with follow-up data of the recent Type IIb SN2019lqo and Type Ib SN2020fkb that occurred in the LIRG system Arp299 with host extinctions of $A_V=2.1^{+0.1}_{-0.3}$ and $A_V=0.4^{+0.1}_{-0.2}$ mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find that, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb/Ib/Ic/Ibn) and 15 H-rich (Type II/IIn) CCSNe have different underlying progenitor age distributions, with the H-poor progenitors being younger at 3$sigma$ significance. However, we do note that the available sample sizes of CCSNe and host LIRGs are so far small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages. (abridged)
The dwarf galaxy companions to the Milky Way are unique cosmological laboratories. With luminosities as low as 10^-7 L_MW, they inhabit the lowest mass dark matter halos known to host stars and are presently the most direct tracers of the distribution, mass spectrum, and clustering scale of dark matter. Their resolved stellar populations also facilitate detailed studies of their history and mass content. To fully exploit this potential requires a well-defined census of virtually invisible galaxies to the faintest possible limits and to the largest possible distances. I review the past and present impacts of survey astronomy on the census of Milky Way dwarf galaxy companions, and discuss the future of finding ultra-faint dwarf galaxies around the Milky Way and beyond in wide-field survey data.
We investigate the properties of the galaxies that reionized the Universe and the history of cosmic reionization using the Evolution and Assembly of GaLaxies and their environments (EAGLE) cosmological hydrodynamical simulations. We obtain the evolution of the escape fraction of ionizing photons in galaxies assuming that galactic winds create channels through which 20~percent of photons escape when the local surface density of star formation is greater than $0.1$ M$_odot$ yr$^{-1}$ kpc$^{-2}$. Such threshold behaviour for the generation of winds is observed, and the rare local objects which have such high star formation surface densities exhibit high escape fractions of $sim 10$ percent. In our model the luminosity-weighted mean escape fraction increases with redshift as $bar f_{rm esc}=0.045~((1+z)/4)^{1.1}$ at $z>3$, and the galaxy number weighted mean as $langle f_{rm esc} rangle=2.2times10^{-3}~((1+z)/4)^4$, and becomes constant $approx0.2$ at redshift $z>10$. The escape fraction evolves as an increasingly large fraction of stars forms above the critical surface density of star formation at earlier times. This evolution of the escape fraction, combined with that of the star formation rate density from EAGLE, reproduces the inferred evolution of the filling factor of ionized regions during the reionization epoch ($6<z<8$), the evolution of the post-reionization ($0leq z<6$) hydrogen photoionisation rate, and the optical depth due to Thomson scattering of the cosmic microwave background photons measured by the Planck satellite.
This presentation reviews Chandras major contribution to the understanding of nearby galaxies. After a brief summary on significant advances in characterizing various types of discrete X-ray sources, the presentation focuses on the global hot gas in and around galaxies, especially normal ones like our own. The hot gas is a product of stellar and AGN feedback -- the least understood part in theories of galaxy formation and evolution. Chandra observations have led to the first characterization of the spatial, thermal, chemical, and kinetic properties of the gas in our Galaxy. The gas is concentrated around the Galactic bulge and disk on scales of a few kpc. The column density of chemically-enriched hot gas on larger scales is at least an order magnitude smaller, indicating that it may not account for the bulk of the missing baryon matter predicted for the Galactic halo according to the standard cosmology. Similar results have also been obtained for other nearby galaxies. The X-ray emission from hot gas is well correlated with the star formation rate and stellar mass, indicating that the heating is primarily due to the stellar feedback. However, the observed X-ray luminosity of the gas is typically less than a few percent of the feedback energy. Thus the bulk of the feedback (including injected heavy elements) is likely lost in galaxy-wide outflows. The results are compared with simulations of the feedback to infer its dynamics and interplay with the circum-galactic medium, hence the evolution of galaxies.
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