Abstract The detection of the accelerated expansion of the Universe has been one of the major breakthroughs in modern cosmology. Several cosmological probes (Cosmic Microwave Background, Supernovae Type Ia, Baryon Acoustic Oscillations) have been studied in depth to better understand the nature of the mechanism driving this acceleration, and they are being currently pushed to their limits, obtaining remarkable constraints that allowed us to shape the standard cosmological model. In parallel to that, however, the percent precision achieved has recently revealed apparent tensions between measurements obtained from different methods. These are either indicating some unaccounted systematic effects, or are pointing toward new physics. Following the development of CMB, SNe, and BAO cosmology, it is critical to extend our selection of cosmological probes. Novel probes can be exploited to validate results, control or mitigate systematic effects, and, most importantly, to increase the accuracy and robustness of our results. This review is meant to provide a state-of-art benchmark of the latest advances in emerging “beyond-standard” cosmological probes. We present how several different methods can become a key resource for observational cosmology. In particular, we review cosmic chronometers, quasars, gamma-ray bursts, standard sirens, lensing time-delay with galaxies and clusters, cosmic voids, neutral hydrogen intensity mapping, surface brightness fluctuations, stellar ages of the oldest objects, secular redshift drift, and clustering of standard candles. The review describes the method, systematics, and results of each probe in a homogeneous way, giving the reader a clear picture of the available innovative methods that have been introduced in recent years and how to apply them. The review also discusses the potential synergies and complementarities between the various probes, exploring how they will contribute to the future of modern cosmology. 

/pdf/unveiling-the-universe-with-emerging-cosmological-probes-3rps7k9o.pdf

Unveiling the Universe with emerging cosmological probes

We describe the scientific goals and survey design of the First Large Absorption Survey in HI (FLASH), a wide field survey for 21-cm line absorption in neutral atomic hydrogen (HI) at intermediate cosmological redshifts. FLASH will be carried out with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope and is planned to cover the sky south of $\delta \approx +40$deg at frequencies between 711.5 and 999.5MHz. At redshifts between $z = 0.4$ and $1.0$ (look back times of 4 - 8Gyr), the HI content of the Universe has been poorly explored due to the difficulty of carrying out radio surveys for faint 21-cm line emission and, at ultra-violet wavelengths, space-borne searches for Damped Lyman-$\alpha$ absorption in quasar spectra. The ASKAP wide field of view and large spectral bandwidth, in combination with a radio-quiet site, will enable a search for absorption lines in the radio spectra of bright continuum sources over 80% of the sky. This survey is expected to detect at least several hundred intervening 21-cm absorbers, and will produce an HI-absorption-selected catalogue of galaxies rich in cool, star-forming gas, some of which may be concealed from optical surveys. Likewise, at least several hundred associated 21-cm absorbers are expected to be detected within the host galaxies of radio sources at $0.4 < z < 1.0$, providing valuable kinematical information for models of gas accretion and jet-driven feedback in radio-loud active galactic nuclei. FLASH will also detect OH 18-cm absorbers in diffuse molecular gas, megamaser OH emission, radio recombination lines, and stacked HI emission.

The First Large Absorption Survey in HI (FLASH): I. Science Goals and Survey Design

By cross-correlating an archival sample of 170 BL Lacs with a 2 year Fermi/LAT AGN sample, we have compiled a sample of 100 BL Lacs with Fermi detection (FBLs) and a sample of 70 non-Fermi BL Lacs (NFBLs). We compared various parameters of FBLs with those of NFBLs, including the redshift, the low-frequency radio luminosity at 408 MHz (L-408 MHz), the absolute magnitude of host galaxies (M-host), the polarization fraction from the NVSS survey (P-NVSS), the observed arcsecond scale radio core flux at 5 GHz (F-core), and the jet Doppler factor. All these parameters are directly measured or derived from available data in the literature. We found that the Doppler factor is on average greater in FBLs than in NFBLs, and the Fermi gamma-ray detection rate is higher in sources with higher Doppler factor. In contrast, there are no significant differences in terms of the intrinsic parameters of redshift, L-408 MHz, M-host, and P-NVSS. FBLs seem to have a higher probability of exhibiting measurable proper motion. These results strongly indicate a stronger beaming effect in FBLs compared to NFBLs. The radio core flux is found to be strongly correlated with gamma-ray flux, which remains after excluding the common dependence of the Doppler factor. At the fixed Doppler factor, FBLs have systematically larger radio core flux than NFBLs, implying lower gamma-ray emission in NFBLs since the radio and gamma-ray flux are significantly correlated. Our results indicate that the Doppler factor is an important parameter of gamma-ray detection, that the non-detection of gamma-ray emission in NFBLs is probably due to low beaming and/or low intrinsic gamma-ray flux, and the gamma-rays are very likely produced cospatially with the arcsecond-scale radio core radiation and mainly through the SSC process.

/pdf/why-are-some-bl-lacertaes-detected-by-fermi-but-others-not-4lhj97x1tg.pdf

Why are some BL Lacertaes detected by FErmi,but others not

We describe the scientific goals and survey design of the First Large Absorption Survey in HI (FLASH), a wide field survey for 21-cm line absorption in neutral atomic hydrogen (HI) at intermediate cosmological redshifts. FLASH will be carried out with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope and is planned to cover the sky south of $\delta \approx +40$deg at frequencies between 711.5 and 999.5MHz. At redshifts between $z = 0.4$ and $1.0$ (look back times of 4 - 8Gyr), the HI content of the Universe has been poorly explored due to the difficulty of carrying out radio surveys for faint 21-cm line emission and, at ultra-violet wavelengths, space-borne searches for Damped Lyman-$\alpha$ absorption in quasar spectra. The ASKAP wide field of view and large spectral bandwidth, in combination with a radio-quiet site, will enable a search for absorption lines in the radio spectra of bright continuum sources over 80% of the sky. This survey is expected to detect at least several hundred intervening 21-cm absorbers, and will produce an HI-absorption-selected catalogue of galaxies rich in cool, star-forming gas, some of which may be concealed from optical surveys. Likewise, at least several hundred associated 21-cm absorbers are expected to be detected within the host galaxies of radio sources at $0.4 < z < 1.0$, providing valuable kinematical information for models of gas accretion and jet-driven feedback in radio-loud active galactic nuclei. FLASH will also detect OH 18-cm absorbers in diffuse molecular gas, megamaser OH emission, radio recombination lines, and stacked HI emission. 

/pdf/the-first-large-absorption-survey-in-h-scp-i-scp-flash-i-ddz83t8l.pdf

The First Large Absorption Survey in H <scp>i</scp> (FLASH): I. Science goals and survey design

We present the first search for the 5.29 GHz methanimine (CH2 NH) 110  − 111 transition toward a sample of galaxy nuclei. We target seven galaxies that host compact obscured nuclei (CONs) with the Karl G. Jansky Very Large Array. These galaxies are characterized by Compton-thick cores. CH2 NH emission is detected toward six CONs. The brightness temperatures measured toward Arp 220 indicate maser emission. Isotropic luminosities of the CH2 NH transition, from all sources where it is detected, exceed 1 L ⊙ and thus may be considered megamasers. We also detect formaldehyde (H2 CO) emission toward three CONs. The isotropic CH2 NH luminosities are weakly correlated with the infrared luminosity of the host galaxy and strongly correlated with OH megamaser luminosities from the same galaxies. Non-local thermodynamic equilibrium radiative transfer models suggest that the maser is pumped by the intense millimeter-to-submillimeter Our study suggests that CH2 NH megamasers are linked to the nuclear processes within 100 pc of the Compton-thick nucleus within CONs.

Discovery of methanimine (CH2NH) megamasers toward compact obscured galaxy nuclei

We present a pilot study of extragalactic HI 21-cm absorption lines using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We observed 5 continuum sources with HI absorption features firstly identified in the 40% data release of the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFA) Survey (ALFALFA), including two systems later detected by the Westerbork Synthesis Radio Telescope (WSRT). Most of our observations were carried out during the FAST commissioning phase, and we have tested different observing modes, as well as data reduction methods, to produce the best spectra. Our observations successfully confirmed the existence of HI absorption lines in all these systems, including two sources that were marginally detected by ALFALFA. We fitted the HI profiles with single or double of Gaussian functions, and calculated the HI column densities of each source. The HI absorption profiles obtained by FAST show much higher spectral resolution and higher S/N ratio than the existing data in the literature, thus demonstrating the power of FAST in revealing detailed structures of HI absorption lines. Our pilot observations and tests have enabled us to develop a strategy to search for HI absorption sources using the data from the FAST extragalactic HI survey, which is one of the key projects undertaken at FAST. We expect that over 1,500 extragalactic HI absorbing systems could be detected with survey data, based on sensitivity level we achieved in pilot observations.

Extragalactic H i 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope

We present the results of EVN and MERLIN 5 GHz observations of nine ultra-high-energy synchrotron peak BL Lacs (UHBLs) selected as all BL Lacs with \textbf{log ($\nu_{\rm peak}/ \rm Hz)>20$} from Nieppola et al.. The radio structure was investigated for these sources, in combination with the available VLBA archive data. We found that the core-jet structure is detected in five sources, while four sources only have a compact core on pc scale. The core of all sources shows high brightness temperature (with mean and median values \textbf{log ($T_{\rm b} / {\rm K}) \sim11$}, which implies that the beaming effect likely present in all sources. When the multi-epoch VLBI data are available, we found no significant variations either for core or total flux density in two sources (2E 0414+0057 and EXO 0706.1+5913), and no evident proper motion in 2E 0414+0057, while the superluminal motion is likely detected in EXO 0706.1+5913. Our sources are found to be less compact than the typical HBLs in Giroletti et al, by comparing the ratio of the VLBI total flux to the core flux at arcsec scale. Combining all our results, we propose that the beaming effect might be present in the jets of UHBLs, however, it is likely weaker than that of typical HBLs. Moreover, we found that UHBLs could be less Doppler beamed versions of HBLs with similar jet power, by comparing the distribution of redshift, and radio luminosities. The results are in good consistence with the expectations from our previous work.

/pdf/the-radio-structure-of-ultra-high-energy-synchrotron-peak-bl-2db3em0yg2.pdf

The radio structure of ultra-high-energy synchrotron peak BL Lacs

We present the results of European Very Long Baseline Interferometry Network (EVN) and Multi-Element Radio Linked Interferometer Network (MERLIN) 5-GHz observations of nine ultra-high-energy synchrotron-peak BL Lacs (UHBLs), consisting of all BL Lacs with log?(?peak/Hz) > 20 from the work of Nieppola et al. The radio structure was investigated for these sources, in combination with available Very Long Baseline Array (VLBA) archive data. We found that a corejet structure is detected in five sources, while four sources only have a compact core at the pc scale. The cores of all sources show high brightness temperature (with mean and median values log?(Tb/K) 11), which implies that the beaming effect is likely present in all sources. When multi-epoch Very Long Baseline Interferometry (VLBI) data are available, we find no significant variations for either core or total flux density in two sources (2E 0414+0057 and EXO 0706.1+5913) and no evident proper motion in 2E 0414+0057, while superluminal motion is likely detected in EXO 0706.1+5913. Our sources are found to be less compact than the typical high-frequency peaked BL Lac objects (HBLs) of Giroletti et al., by comparing the ratio of the VLBI total flux and the core flux at the arcsec scale. Combining all our results, we propose that the beaming effect might be present in the jets of UHBLs; however, it is likely weaker than that for typical HBLs. Moreover, we found by comparing the distributions of redshift and radio luminosity that UHBLs could be less Doppler-beamed versions of HBLs with similar jet power. These results are in good consistence with the expectations of our previous work.

/pdf/the-radio-structure-of-ultra-high-energy-synchrotron-peak-bl-3hscmd2iws.pdf

The radio structure of ultra-high-energy synchrotron-peak BL Lacs

Previous observations have shown that the distribution of 36.2-GHz class I methanol megamaser (MM) emission in Arp 220 is highly correlated with the diffuse X-rays. On this basis it was suggested that methanol MM may be produced either by the effects of galactic-outflow-driven shocks and/or cosmic rays. Here we report the results of a single-dish survey undertaken with the Greenbank Telescope (GBT) to improve our understanding of the pumping conditions of extragalactic class I methanol masers and their relationship to starburst and feedback processes within the host galaxies, towards a sample which includes 16 galaxies which show both extended soft X-ray emission, and either OH or H2O MM emission. Large baseline ripples in the GBT spectra limited our results to tentative detections towards 11 of the target galaxies. Analysis of these tentative detections shows that there are significant correlations between the methanol intensity and the host-galaxy infrared, radio and OH MM emission, but no correlation with the X-ray and H2O MM emission. Some sources show methanol emission significantly offset from the systemic velocity of the galaxy (by up to 1000 km s−1) and we propose that these are associated with galactic-scale outflows from active galactic nuclei (AGNs) feedback. The combined observational properties suggest that class I methanol MMs are related to significant starburst and molecular outflow activity and hence may provide a potential probe of AGN feedback and starburst processes in the host galaxies.

/pdf/class-i-methanol-megamasers-a-potential-probe-of-starburst-27k9t7wik4.pdf

Class I methanol megamasers: a potential probe of starburst activity and feedback in active galaxies

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Extragalactic H i 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope

The radio structure of ultra-high-energy synchrotron peak BL Lacs

The radio structure of ultra-high-energy synchrotron-peak BL Lacs

Class I methanol megamasers: a potential probe of starburst activity and feedback in active galaxies