arXiv subjects

Juliana Saponara

Publications and source records attributed to Juliana Saponara.

4 recordsLinked to original sources

arXiv2026

HI Observations of Baryon-Dominated Dwarf Galaxy Candidates

We present resolved HI observations of six dwarf galaxies drawn from a sample of baryon-dominated dwarf galaxy (BDDG) candidates previously identified using global HI spectra from ALFALFA and optical inclinations from SDSS, both of which suffer from systematic uncertainties in irregular dwarf galaxies. Using uGMRT interferometric observations, we obtain high-resolution HI cubes that enable more reliable determination of their geometry, circular velocity, and dynamical mass. We find that optical axial ratios systematically underestimate true disc thickness, inflating inclinations and underestimating rotation velocities in earlier work. Our HI-derived axial ratios and kinematic position angles yield larger inclination corrections and hence larger dynamical masses. Four of these galaxies, UGC 6438, UGC 7983, AGC 191707, and AGC 733302, appear dark-matter deficient. The latter three of these four exhibit high baryon enhancement efficiency factor (ratio of baryon mass accumulated by a halo to the maximum expected value for its halo mass) exceeding 50%, with AGC 191707 appearing formally super-efficient. Only UGC 9500 and AGC 220901 are consistent with being dark-matter dominated. Two of these high-efficiency dwarf galaxies lie in relatively isolated environments, showing no clear signatures of tidal disturbance or stripping, making their dark-matter deficiency difficult to reconcile with standard $ΛCDM$ expectations for low-mass halos. Our results underscore the importance of resolved HI kinematics in confirming genuine BDDGs and suggest that more such systems may exist. Identifying a larger sample is essential for assessing their implications for baryon-halo coupling and structure formation within the $ΛCDM$ paradigm.

astro-ph.GA↗

arXiv2025

Radio study of the colliding wind binary HD93129A near periastron and its surroundings

HD93129A is an O+O stellar system whose CWR has been mapped by high angular resolution observations at cm wavelengths. The synchrotron nature of the radio emission confirms its particle accelerator status. According to astrometric measurements since 1996, the system has an orbital period of ~120 yr and recently went through its periastron passage. We characterize the radio emission during the epoch of periastron passage, when the particle density and the local magnetic energy density in the CWR increase. We monitored HD93129A and surroundings at 2.1, 5.5 and 9 GHz with the ATCA over 17 months, with a ~2-month cadence. Previous ATCA data and data collected using other radio observatories were also included. We obtained radio light curves in subbands per band per epoch. The flux densities show an average rise of a factor four from 2003 to 2018, with the caveat that the 2009-2018 time lapse is devoid of data, and a similar decay between 2018 to 2020. We fit the spectral energy distribution of quasi-simultaneous data at three epochs and find that the magnetic-to-thermal pressure ratio does not remain constant along the orbit, possible suggesting magnetic field amplification close to periastron. In the 2019 epoch, we estimate a magnetic field strength of ~1.1G in the apex of the CWR. The evolution of the SED and spectral index is also presented. By combining ATCA and ASKAP images a spectral index map was obtained in an area of 30' size. The radio emission in the direction of other massive binary systems in the field (WR22, WR25 and HD93250) was measured and briefly discussed. Intensive radio monitoring allows us to track the evolution of physical conditions in the shocks. The general trend of decreasing emission of HD93129A in the high-frequency bands in 2019-2020 suggests that the system is at post-periastron, consistent with model predictions. (Abridged)

astro-ph.SR↗

arXiv2019

Investigation of the WR 11 field at decimeter wavelengths

The massive binary system WR11 has been recently proposed as the counterpart of a Fermi source. If correct, it would be the second colliding wind binary detected in GeV gamma-rays. However, the reported flux measurements from 1.4 to 8.64GHz fail to establish the presence of non-thermal (synchrotron) emission from this source. Moreover, WR11 is not the only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of which present strong non-thermal radio emission. We conducted "-resolution observations towards WR11 at very low frequencies (150 to 1400~MHz) where the NT emission is expected to dominate, and present a catalog of more than 400 radio-emitters, among which a significant part is detected at more than one frequency, including limited spectral index information. A search for counterparts for this last group pointed at MOST0808-471, a source 2' away from WR11, as a promising candidate for high-energy emission, with resolved structure along 325 - 1390 MHz. For it, we reprocessed archive interferometric data up to 22.3 GHz and obtained a non-thermal radio spectral index of -0.97 +- 0.09. However, multiwavelength observations of this source are required to establish its nature and to assess whether it can produce (part of) the observed gamma-rays. WR11 spectrum follows a spectral index of 0.74 +- 0.03 from 150 to 230 GHz, consistent with thermal emission. We interpret that any putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheres of the individual components. Notwithstanding, the new radio data allowed to derive a mass loss rate of 0.000025 Mo/yr, which, according to the latest models for gamma-ray emission in WR 11, would suffice to provide the required kinetic power to feed non-thermal radiation processes.

astro-ph.SR↗

arXiv2017

HI debris in the IC 1459 galaxy group

We present HI synthesis imaging of the giant elliptical galaxy IC 1459 and its surroundings with the Australia Telescope Compact Array (ATCA). Our search for extended HI emission revealed a large complex of HI clouds near IC 1459, likely the debris from tidal interactions with neighbouring galaxies. The total HI mass ($\sim 10^9$\Msun) in the detected clouds spans 250 kpc from the north-east of the gas-rich spiral NGC 7418A to the south-east of IC 1459. The extent and mass of the HI debris, which shows rather irregular morphology and kinematics, are similar to those in other nearby groups. Together with HI clouds recently detected near two other IC 1459 group members, namely IC 5270 and NGC 7418, using Phased-Array Feeds (PAFs) on the Australian Square Kilometer Array Pathfinder (ASKAP), the detected debris make up a significant fraction of the group's intergalactic medium.

astro-ph.GA↗