Chandra Observation of the Edge-on Spiral NGC 5775: Probing the Hot Galactic Disk/Halo Connection

TL;DR

This study uses multi-wavelength data, including Chandra X-ray observations, to analyze the hot gas and disk/halo interactions in the edge-on galaxy NGC 5775, revealing extraplanar features and a relation between X-ray intensity and star formation.

Contribution

First detailed multi-wavelength analysis of hot gas and disk/halo connection in NGC 5775, highlighting extraplanar features and X-ray-star formation relation.

Findings

Detection of 27 X-ray sources, including an ultra-luminous one.

Identification of extraplanar features like shells and blobs.

Characterization of halo hot gas with a two-temperature plasma.

Abstract

We study the edge-on galaxy NGC 5775, utilizing a 58.2 ks {\sl Chandra} ACIS-S observation together with complementary {\sl HST} ACS, {\sl Spitzer} IRAC and other multi-wavelength data sets. This edge-on galaxy, with its disk-wide active star formation, is particularly well-suited for studying the disk/halo interaction on sub-galactic scales. We detect 27 discrete X-ray sources within the $D_{25}$ region of the galaxy, including an ultra-luminous source with a 0.3-7 keV luminosity of $\sim7\times10^{40}\rm ergs s^{-1}$. The source-removed diffuse X-ray emission shows several prominent extraplanar features, including a $\sim10\rm kpc$ diameter ``shell-like'' feature and a ``blob'' reaching a projected distance of $\sim25\rm kpc$ from the galactic disk. The bulk of the X-ray emission in the halo has a scale height of $\sim$1.5 kpc and can be characterized by a two-temperature optically thin thermal plasma with temperatures of $\sim$ 0.2 and 0.6 keV and a total 0.3-2 keV luminosity of $\sim3.5\times10^{39}\rm ergs s^{-1}$. The high-resolution, multi-wavelength data reveal the presence of several extraplanar features around the disk, which appear to be associated with the in-disk star formation. We suggest that hot gas produced with different levels of mass loading can have different temperatures, which may explain the characteristic temperatures of hot gas in the halo. We have obtained a sub-galactic scale X-ray-intensity-star formation relation, which is consistent with the integrated version in other star forming galaxies.