arXiv subjects

Mary Rickel

Publications and source records attributed to Mary Rickel.

4 recordsLinked to original sources

arXiv2026

Diffuse HI emission in the circumgalactic medium of NGC891 and NGC4565 - III: azimuthal profiles

Diffuse HI emission in the circumgalactic medium (CGM) of NGC891 and NGC4565 has been previously shown to trace an inflow along minor axes pointings and to co-rotate with the HI disk along major axes pointings out to ~100 kpc (Das2020b,Das2024a). To obtain a 360$^\circ$ view of the inner neutral CGM ($\rm < 25 kpc$ for NGC891, $\rm < 30 kpc$ for NGC4565), we perform deep stare observations with the Green Bank Telescope (GBT) along the off-axes, 45$^\circ$ between principal axes, achieving a 5$\sigma$ column density sensitivity of $1.1-1.2 x 10^{17} \rm cm^{-2}$ over a 20 kms$^{-1}$ velocity width. While detecting HI emission in the inner CGM with single-dish telescopes is common, separating the true CGM emission from disk contamination is extremely challenging and has so far been largely unsuccessful. To achieve that, we compare our single-dish detections to deep interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) HALOGAS survey, and improve upon our previous methods by incorporating velocity offset corrections and channel-wise brightness-temperature scaling. We find that $30-38$ % and $18-28$ % of the emission detected by the GBT cannot be explained by WSRT in NGC891 and NGC4565, respectively, implying a true CGM detection. There is $4-6$ ($3-7$) times more HI along the off-axes than major (minor) axes, nullifying the common assumption of azimuthal symmetry of the neutral CGM. The velocity profile of the diffuse inner CGM suggests a lagged co-rotation with the HI disk in both galaxies. This exercise illustrates the power of deep observation and careful cross-instrument comparisons to characterize the diffuse HI in the CGM.

astro-ph.GA↗

arXiv2026

The GOLIATH Survey: OVI Absorption Reveals CGM Evolution through the Starburst-to-Quiescent Transition in Massive Galaxies

We present the GOLIATH survey (Galaxies, Outflows, and the Lifecycle of Immense, Active, Transforming Halos), a study of the multiphase circumgalactic medium (CGM) of massive ($\langle\log M_\star/M_\odot\rangle \approx 11$), blue ($u-r < 1.65$) starburst and post-starburst galaxies at $\langle z\rangle \approx$ 0.43. This work characterizes the warm-hot CGM through OVI absorption in the inner halo ($R/R_{\rm vir} \leq 0.6$) of these rare systems. Across the star-forming population, OVI column density rises by nearly 1~dex from $\log M_\star/M_{\odot} \sim 8$ to $\sim 11.5$ and increases with specific star-formation rate (sSFR). Two GOLIATH galaxies with the highest sSFR show the strongest CGM OVI absorption ($\log N_{\rm O\,VI}[\rm cm^{-2}] \gtrsim 15$). In the $\log M_\star/M_{\odot} = [11,12)$ inner-CGM region, massive star-forming galaxies exceed quiescent galaxies on average by a factor of $\sim 3$ in OVI column density and $\sim 1.5$~dex in CGM OVI mass ($\log(M_{\rm O\, VI}/M_\odot) \approx 7.3$ versus $\approx 5.8$), with covering fractions roughly three times higher (62.5% versus 24% at $\log N_{\rm O\,VI}[\rm cm^{-2}] \geq 14$). The OVI line widths and column densities are consistent with feedback-driven radiative cooling, in which outflow shocks heat the CGM and the gas cools back through the OVI window; the short cooling time, $t_{\rm cool} \sim 10$-$100$~Myr, requires continuous replenishment by active feedback to sustain this reservoir. The residual OVI in quiescent systems may arise from ambient gas at the high-temperature end of the cooling curve. OVI thus traces feedback on short timescales and probes the star-forming--quiescent transition at $\log M_\star/M_{\odot} \gtrsim 11$.

astro-ph.GA↗

arXiv2025

The Merging Galaxy Cluster Environment Affects the Morphology of Radio-AGN

It has previously been found that the galaxy cluster environment can affect the fueling and evolution of Active Galactic Nuclei (AGN). This work examines the effect of the merging cluster environment on the properties of radio-AGN by comparing the radio morphology of cluster members in a sample of four merging and eight relaxed galaxy clusters at low redshift (z<0.2). Using 144-MHz data from the LOFAR Two-metre Sky Survey (LoTSS) and Zooniverse, we classify the radio morphology of the radio-detected cluster members using the following morphology classes: compact, compact extended, extended, jetted, and disturbed. We find that the merging cluster environment has a statistically significant, higher population proportion of disturbed (bent and head tail) sources, indicating that the merging environment can affect the morphology of cluster radio-AGN. We also investigate the number of AGN that are detected in the radio data only, and the number that are detected in both the radio and optical data in mergers and non-mergers. We find that the merging cluster environment has a higher population proportion of AGN that are identified only as radio-AGN compared to AGN that are identified as both radio and optical AGN. Overall, we find that the merging environment affects certain radio-AGN (disturbed and only radio identified AGN), but not all.

astro-ph.GA↗

arXiv2023

Detection of diffuse HI emission in the circumgalactic medium of NGC891 and NGC4565 -- II

We probe the neutral circumgalactic medium (CGM) along the major axes of NGC891 and NGC4565 in 21-cm emission out to $\gtrsim 100$kpc using the Green Bank Telescope (GBT), extending our previous minor axes observations. We achieve an unprecedented $5σ$ sensitivity of $6.1\times 10^{16}$ cm$^{-2}$ per 20 km s$^{-1}$ velocity channel. We detect HI with diverse spectral shapes, velocity widths, and column densities. We compare our detections to the interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) obtained as part of the HALOGAS survey. At small impact parameters, $> 31-43\%$ of the emission detected by the GBT cannot be explained by emission seen in the WSRT maps, and it increases to $> 64-73\%$ at large impact parameters. This implies the presence of diffuse circumgalactic HI. The mass ratio between HI in the CGM and HI in the disk is an order of magnitude larger than previous estimates based on shallow GBT mapping. The diffuse HI along the major axes pointings is corotating with the HI disk. The velocity along the minor axes pointings is consistent with an inflow and/or fountain in NGC891 and an inflow/outflow in NGC4565. Including the circumgalactic HI, the depletion time and the accretion rate of NGC4565 are sufficient to sustain its star formation. In NGC891, most of the required accreting material is still missing.

astro-ph.GA↗