arXiv subjects

Julian Shapiro

Publications and source records attributed to Julian Shapiro.

3 recordsLinked to original sources

arXiv2026

CHASE Spectral Survey I: Measuring Contamination in the Color-selected J-region Asymptotic Giant Branch Distance Indicator

The J-region asymptotic giant branch (JAGB) method for distance measurements uses the near uniform luminosity of carbon-rich AGB stars as a standard candle. Its application rests on an assumed but rarely examined premise: the stars contained in the JAGB color-magnitude selection box are primarily carbon-rich AGB stars. We investigate the purity of the photometric selection in the Milky Way with an optical spectroscopic survey (~3590-7150 $\mathring{A}$) called CHASE (Carbon stars, Hubble tension, And Spectroscopic Exploration of JAGB populations) using the Shane 3 m telescope at Lick Observatory. These stars are classified using molecular bandhead step indices, which recover 100% of known classifications. We report the observations of 76 stars (54 within the standard JAGB selection box of 1.5 < J - K < 2.0 mag) and find only 13 of 54 stars are carbon-rich, a 76$\pm$6 oxygen-rich contamination under blind photometric selection. This contamination remains high (71%) even within $\pm$0.4 mag of the JAGB peak itself, showing it is not confined to the edges of the selection box. This inhomogeneity may explain why recent literature find field-to-field and methodological variations of 0.1-0.2 mag that now dominate its systematic error budget. These variations could be caused, in part, by inhomogeneous stellar populations that consist of differing spectral types, and hence differing mean magnitudes.

astro-ph.GA↗

arXiv2026

Discovery of Isolated, Quenched Candidate Backsplash Dwarf Galaxies near M101

I report the discovery of three faint, semi-resolved quiescent candidate dwarf galaxies, which are potential backsplash galaxies associated with the nearby spiral M101 ($D \sim 6.7 \,\mathrm{Mpc}$). The galaxies are cataloged as Shapiro DG-I/MAGE1412+5650, Shapiro DG-II, and Shapiro DG-III. Sha DG-I is concurrently discovered in ID-MAGE. The backsplash candidates lie in a magnitude range $M_V\sim-7.3$ to $-8.1$, and half-light radii $r_h\sim110-140\,\mathrm{pc}$. Hydrodynamical simulations suggest a population of backsplash galaxies that have been environmentally stripped by interactions with a host and ejected from the system, though they have not yet been definitively observed in the local universe. Initial distance estimates are determined using surface brightness fluctuations in Sérsic model-subtracted CFHTLS and HSC archival images. The galaxies are not detected in GALEX, or H$α$ for Sha DG-I/MAGE1412+5650, providing upper limits on their SFR history. The provisional distances and quiescence of the dwarf candidates are consistent with a potential backsplash nature, though HST/JWST follow-up are necessary for stronger constraints, and to probabilistically distinguish from cosmic web stripping. Sha DG-II is alternatively a possible satellite of NGC 5585. Abundance models of satellites based on halo masses, which can be extended to model backsplash galaxies, will enable important consistency tests of $Λ\mathrm{CDM}$ with upcoming surveys, e.g., LSST. This is briefly explored in the context of the M101 group.

astro-ph.GA↗

arXiv2026

Discovery of Optical Filaments in the North Polar Spur/eROSITA Bubble

I report the discovery of optical filaments in H$α$, [O III], and [S II], coincident with $144\,\mathrm{MHz}$ structure, associated with the North Polar Spur (NPS) region of the eROSITA bubbles. The optical emission is identified in the Northern Sky Narrowband Survey, and contains distinct structure and potentially elevated $\text{[S II]}/\mathrm{H}α$ relative to typical high-$b$ outflows from the warm ionized medium (WIM). $Δ$-variance and power spectrum analysis of the NPS H$α$ shows a preference for filaments on the scale of lag $L\approx0.6^{\circ}$. The optical and $144\,\mathrm{MHz}$ emission peaks in intensity in an interior region of the NPS, aligned with surrounding Galactic magnetized structures, and also shows fainter signal at the eROSITA bubble edge. The required power to produce the background-subtracted $I_{\mathrm{H}α}=1.85\pm1.04\,\mathrm{R}$ emission is $P_\mathrm{req}\approx5\mathrm{-}12\times10^{41}\,\mathrm{erg\,s}^{-1}$, comfortably exceeded by AGN jet models, plausible for AGN hot accretion flow and star formation ring models, and disfavoring star formation driven winds.

astro-ph.GA↗