arXiv subjects

Andrea Tarchi

Publications and source records attributed to Andrea Tarchi.

7 recordsLinked to original sources

arXiv2026

Advancing extragalactic spectral line studies with the Square Kilometre Array Observatory

We present an overview of the Square Kilometre Array Observatory (SKAO) science potential in the area of extragalactic spectral lines besides 21-cm neutral hydrogen. It highlights the main points from the SKAO Science Book chapters on individual topics, but is augmented by additional prospects. The SKAO will push studies and use of masers, kilomasers, megamasers, molecular and radio-recombination-line emission and absorption to a wider variety of environments, including to very high redshift where it may detect the first molecule (HeH$^+$). It will open the door to measurements of hydrogen and helium isotopes, probing the conditions for star formation and Big Bang nucleosynthesis. While the planned SKAO of the 2030s (AA*) is destined to forge major progress, an SKAO as initially envisaged (AA4) will truly transform the landscape, and an extension towards higher frequencies (up to 24 GHz) would enable water maser and ammonia surveys in nearby galaxies and systematic molecular gas inventories at redshift 5.

astro-ph.GA↗

arXiv2026

Boosting Water Maser Studies in AGN with the SKA

Extragalactic water maser sources are unique tools to derive fundamental physical quantities of the host galaxies. In nearby and distant active galactic nuclei (AGN), water masers are used to determine the geometry of accretion disks around super-massive black holes, precise black hole masses, and standard-candles-independent distances to the host galaxy. In addition, they allow detailed studies of the interaction between nuclear jets/outflows and the interstellar medium, providing clues on AGN feedback mechanisms. So far, however, extragalactic maser searches have yielded detection rates of few percent, and only relatively few maser sources have been found, mostly in the nearby Universe. Because of its unprecedented sensitivity, the SKA will allow to significantly increase the number of known water maser sources especially in the more distant Universe. This will lead to the chance of performing statistically-relevant studies of the maser phenomenon (and its occurrence), derive extragalactic maser luminosity functions and, ultimately, to perform the aforementioned studies for larger samples and up to cosmological distances. In this Chapter, we will provide a quantitative analysis of the expected number of new extragalactic water maser sources already at the reach of the SKA-Mid telescope (in AA4 configuration) through targeted and blinds surveys. In addition, we will discuss the main requirements for the upcoming SKA design, in terms of baselines and frequency coverage, that may maximize the exploitation of such wealth of new targets, allowing a true step forward in AGN-related maser science.

astro-ph.GA↗

arXiv2020

Water megamaser emission in hard X-ray selected AGN

Water megamaser emission at 22 GHz has proven to be a powerful tool for astrophysical studies of AGN allowing an accurate determination of the central black hole mass and of the accretion disc geometry and dynamics. However, after searches among thousands of galaxies, only ~ 200 of them have shown such spectroscopic features, most of them of uncertain classification. In addition, the physical and geometrical conditions under which maser activates are still unknown. In this work we aim at characterizing the occurrence of water maser emission in an unbiased sample of AGN, investigating the relation with the X-ray properties and the possible favorable geometry needed to detect water maser. We have searched for 22 GHz maser emission in a hard X-ray selected sample of AGN, taken from the INTEGRAL/IBIS survey above 20 keV. Of the 380 sources in the sample, only half have water maser data. We have also considered a sub-sample of 87 sources, volume limited, for which we obtained new Green Bank Telescope and Effelsberg observations (for 35 sources), detecting one new maser and increasing its radio coverage to 75%. The detection rate of water maser emission in the total sample is 15+/-3%, this fraction raises up to 19+/-5% for the complete sub-sample, especially if considering type 2 and Compton thick AGN. These results demonstrate that the hard X-ray selection may significantly enhance the maser detection efficiency over comparably large optical/infrared surveys. A possible decline of the detection fraction with increasing luminosity might suggest that an extreme luminous nuclear environment does not favour maser emission. The large fraction of CT AGN with water maser emission could be explained in terms of geometrical effects, being the maser medium the very edge-on portion of the obscuring medium.

astro-ph.GA↗

arXiv2013

High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA

An international consortium is presently constructing a beamformer for the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile that will be available as a facility instrument. The beamformer will aggregate the entire collecting area of the array into a single, very large aperture. The extraordinary sensitivity of phased ALMA, combined with the extremely fine angular resolution available on baselines to the Northern Hemisphere, will enable transformational new very long baseline interferometry (VLBI) observations in Bands 6 and 7 (1.3 and 0.8 mm) and provide substantial improvements to existing VLBI arrays in Bands 1 and 3 (7 and 3 mm). The ALMA beamformer will have impact on a variety of scientific topics, including accretion and outflow processes around black holes in active galactic nuclei (AGN), tests of general relativity near black holes, jet launch and collimation from AGN and microquasars, pulsar and magnetar emission processes, the chemical history of the universe and the evolution of fundamental constants across cosmic time, maser science, and astrometry.

astro-ph.IM↗

arXiv2012

AGN and Megamasers

Luminous extragalactic masers are traditionally referred to as the `megamasers'. Those produced by water molecules are associated with accretion disks, radio jets, or outflows in the nuclear regions of active galactic nuclei (AGN). The majority of OH maser sources are instead driven by intense star formation in ultra-luminous infrared galaxies, although in a few cases the OH maser emission traces rotating (toroidal or disk) structures around the nuclear engines of AGN. Thus, detailed maser studies provide a fundamental contribution to our knowledge of the main nuclear components of AGN, constitute unique tools to measure geometric distances of host galaxies, and have a great impact on probing the, so far, paradigmatic Unified Model of AGN.

astro-ph.CO↗

arXiv2009

Molecular Superbubbles and Outflows from Starburst Galaxy NGC 2146

We present results from a deep (1 sigma = 5.7 mJy beam^{-1} per 20.8 km s^{-1} velocity channel) ^{12}CO(1-0) interferometric observation of the central 60" region of the nearby edge-on starburst galaxy NGC 2146 observed with the Nobeyama Millimeter Array (NMA). Two diffuse expanding molecular superbubbles and one molecular outflow are successfully detected. One molecular superbubble, with a size of ~1 kpc and an expansion velocity of ~50 km s^{-1}, is located below the galactic disk; a second molecular superbubble, this time with a size of ~700 pc and an expansion velocity of ~35 km s^{-1}, is also seen in the position-velocity diagram; the molecular outflow is located above the galactic disk with an extent ~2 kpc, expanding with a velocity of up to ~200 km s^{-1}. The molecular outflow has an arc-like structure, and is located at the front edge of the soft X-ray outflow. In addition, the kinetic energy (~3E55 erg) and the pressure (~1 E-12 \pm 1 dyne cm ^{-2}) of the molecular outflow is comparable to or smaller than that of the hot thermal plasma, suggesting that the hot plasma pushes the molecular gas out from the galactic disk. Inside the ~1 kpc size molecular superbubble, diffuse soft X-ray emission seems to exist. But since the superbubble lies behind the inclined galactic disk, it is largely absorbed by the molecular gas.

astro-ph↗

arXiv2004

Chandra Observation of the Starburst Galaxy NGC 2146

We present six monitoring observations of the starburst galaxy NGC 2146 using the Chandra X-ray Observatory. We have detected 67 point sources in the 8'.7 x 8'.7 field of view of the ACIS-S detector. Six of these sources were Ultra-Luminous X-ray Sources, the brightest of which has a luminosity of 5 x 10^{39} ergs s^{-1}. One of the source, with a luminosity of ~1 x 10^{39} ergs s^{-1}, is coincident with the dynamical center location, as derived from the ^{12}CO rotation curve. We suggest that this source may be a low-luminosity active galactic nucleus. We have produced a table where the positions and main characteristics of the Chandra-detected sources are reported. The comparison between the positions of the X-ray sources and those of compact sources detected in NIR or radio does not indicate any definite counterpart. Taking profit of the relatively large number of sources detected, we have derived a logN-logS relation and a luminosity function. The former shows a break at \~10^{-15} ergs cm^{-2} s^{-1}, that we interpret as due to a detection limit. The latter has a slope above the break of 0.71, which is similar to those found in the other starburst galaxies. In addition, a diffuse X-ray emission has been detected in both, soft (0.5--2.0keV) and hard (2.0--10.0keV), energy bands. The spectra of the diffuse component has been fitted with a two (hard and soft) components. The hard power-law component, with a luminosity of ~4 x 10^{39} ergs s^{-1}, is likely originated by unresolved point sources, while the soft component is better described by a thermal plasma model with a temperature of 0.5keV and high abundances for Mg and Si.

astro-ph↗