Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We analyze JWST NIRSpec+MIRI/MRS observations of the infrared (IR) polycyclic aromatic hydrocarbon (PAH) features in the central regions (a at 6 μm; a 440 pc depending on the source) of local luminous IR galaxies. In this work, we examine the effect of nuclear obscuration on the PAH features of deeply obscured nuclei, predominantly found in local luminous IR galaxies, and we compare these nuclei with astar-forming regions. We extend previous work to include shorter wavelength PAH ratios now available with the NIRSpec+MIRI/MRS spectral range. We introduce a new diagnostic diagram for selecting deeply obscured nuclei based on the 3.3 and 6.2 μm PAH features and/or mid-IR continuum ratios at a3 and 5 μm. We find that the PAH equivalent width ratio of the brightest PAH features at shorter wavelengths (at 3.3 and 6.2 μm) is impacted by nuclear obscuration. Although the sample of luminous IR galaxies used in this analysis is relatively small, we find that sources exhibiting a high silicate absorption feature cluster tightly in a specific region of the diagram, whereas star-forming regions experiencing lower extinction levels occupy a different area in the diagram. This demonstrates the potential of this technique to identify buried nuclei. To leverage the excellent sensitivity of the MIRI imager on board JWST, we extend our method of identifying deeply obscured nuclei at higher redshifts using a selection of MIRI filters. Specifically, the combination of various MIRI JWST filters enables the identification of buried sources beyond the local Universe and up to za 3, where other commonly used obscuration tracers such as the 9.7 μm silicate band, are out of the spectral range of MRS. Our results pave the way for identifying distant deeply obscured nuclei with JWST.

Abstract:

Resolved rotation curves (RCs) are the gold-standard measurements for inferring dark matter distributions in Lambda cold dark matter and testing alternative theories of dynamics in galaxies. However, they are expensive to obtain, making them prohibitive for large galaxy samples and at higher redshift. Spatially integrated flux profiles are more accessible and present the information in a different form, but – except in a highly compressed form, as linewidths – have not so far been compared in detail with RCs or employed for dynamical inferences. Here, we study the consistency of RCs and surface density profiles from SPARC with spatially integrated flux profiles from ALFALFA, by combining the resolved properties in a forward model for the flux profile. We define a new metric for asymmetry in the flux profiles, enabling us to cleanly identify those unsuitable for our axisymmetric method. Among all SPARC galaxies the agreement between RCs and flux profiles is satisfactory within the limitations of the data – with most galaxies having an uncertainty-normalized mean squared error (MSE) below 10 – whilst no galaxy deemed symmetric has a MSE above 1.2. Most cases of good agreement prefer an gas dispersion of 13 km s, consistent with resolved studies of gas dispersion from the literature. These results open the door for spatially integrated flux profiles to be used as proxies for spatially resolved dynamics, including a robust appraisal of the degree of asymmetry.