8 GIUGNO 2021 ore 15:00

An ATCA HI survey of the Fornax galaxy cluster

Alessandro Loni (INAF-OAC, Italia)
An ATCA HI survey of the Fornax galaxy cluster

The Fornax galaxy cluster is the nearest representative of the class of low-mass (<10^14Msun) clusters, which are less studied than more massive systems and are an important stepping stone in the hierarchical growth of large scale structure.
In particular, the density of the intra-cluster medium and the velocity dispersion of Fornax are a factor of two lower with respect to those of Virgo, while the galaxy number density is twice as large. Therefore, the balance between gravitational and hydrodynamical interaction is different.
Here, we present results from the most sensitive interferometric blind HI surveys of the Fornax galaxy cluster to date, which provide us with a good opportunity to observe how the Fornax environment affects the evolution of galaxies, as well as study galaxy pre-processing at the cluster's outskirts.
The ATCA HI survey detected emission from 16 galaxies, covering a HI mass range of about 3 orders of magnitude (~10^7-10^10 Msun). We also detected - albeit at the limited resolution of ~1' - a variety of HI disturbed morphologies including asymmetries and offset with respect to optical centers. The comparison with non-cluster galaxies shows that Fornax members are shifted towards lower MHI/Mstar-ratios and have anomalous MHI/ MH2-ratio (ALMA data).
Furthermore, from the joint analysis of the HI content, the SFR and the 3D distribution of Fornax galaxies, we conclude that our HI detections are first-infallers currently at the cluster's outskirts and have been losing HI slowly (typical timescale >~2~Gyr). Further into the inner, hot part of Fornax, no HI is detected, indicating that the removal of HI is faster than a cluster crossing time there (at least down to 10^7Msun).

During the talk, we will also mention the first attempt of using a new Bayesian approach for measuring the HI mass function applied to real data. We aim to infer the HIMF of the Fornax galaxy cluster from the real signal hidden within the noise without co-adding the spectra of HI non-detections.
Finally, we recently obtained 10x more sensitive data with a higher resolution (10'') as part of the MeerKAT Fornax Survey. Although the MeerKAT survey is just 25% complete, it has already detected interesting objects within the Fornax virial radius. Among those, MeerKAT data confirmed the presence of a truncated HI disk: NGC 1436.
We will discuss the state of the art of this object, putting together multiwavelengths
information and recent MeerKAT observations. NGC 1436 might be a case of a SO galaxy in the making where the Fornax environment might have played an important role.



Breve CV di Alessandro Loni:
Alessandro Loni è uno studente di dottorato con base all'INAF Osservatorio Astronomico di Cagliari. Il suo  lavoro nel gruppo di ricerca del Dr. Paolo Serra è focalizzato sull'evoluzione delle galassie Fornax. Il contributo principale riguarda lo studio dell'emissione HI che traccia le interazioni ambientali tra le galassie e l'ambiente denso degli ammassi. Durante il suo dottorato, ha iniziato a lavorare su osservazioni recenti di MeerKAT facenti parti della MeerKAT Fornax Survey. Oltre alla ricerca, Alessandro fa parte di  un gruppo di divulgazione di studenti e ricercatori (IDeAS) che ha lo scopo di mostrare al grande pubblico quanto sia bello e divertente l'Universo!