Year: 2023
Type: article
Abstract: The magnificent bubbles at the Galactic center provide a great channel to understand the effects of feedback on galaxy evolution. The newly discovered eROSITA bubbles show enhanced X-ray emission from the shells around bubbles. Previous works assumed that the X-ray emitting gas in the shells has a single temperature component and that they trace the shock-heated lower-temperature Galactic halo gas. Here we show that the thermal structure of the eROSITA bubble shells is more complex. Using Suzaku observations we find with high confidence that the X-ray emission from the shells is best described by a two-temperature thermal model, one near Galaxy's virial temperature at ~0.2 keV and the other at super-virial temperatures ranging between kT = 0.4-1.1 keV. Furthermore, we show that temperatures of the virial and super-virial components are similar in the shells and in the ambient medium, although the emission measures are significantly higher in the shells. We argue that the X-ray bright eROSITA bubble shells are the signature of compressed isothermal radiative shocks. The age of the bubbles is constrained to 70-130 Myr. This expansion timescale, as well as the observed non-solar Ne/O and Mg/O ratios, favor the stellar feedback models for the formation of the Galactic bubbles, settling a long-standing debate on the origin of the Galactic bubbles.
Source: Nature Astronomy
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: NEARBY LATE-TYPE GALAXIES ARE MISSING A LARGE FRACTION OF THEIR BARYONIC MASS. GALAXIES HAVE ALSO LOST MOST OF THE METALS THAT THEY PRODUCED. COSMOLOGICAL SIMULATIONS OF GALAXY FORMATION SUGGEST THAT A LARGE FRACTION OF THE MISSING BARYONIC MASS AND METALS SHOULD RESIDE IN THE CIRCUM-GALACTIC MEDIUM (CGM) IN A WARM-HOT GAS PHASE AT TEMPERATURES BETWEEN ONE MILLION AND 10 MILLION K. ALTHOUGH THEORETICAL MODELS PREDICT THE EXISTENCE OF THE WARM-HOT GAS IN THE CGM DETECTING AND CHARACTERIZING THE DIFFUSE CGM HAS BEEN DIFFICULT. AT THE EXPECTED TEMPERATURES THE BARYONS ARE IN THE FORM OF HIGHLY IONIZED PLASMA OBSERVABLE IN SOFT X-RAYS. USING OBSERVATIONS FROM CHANDRA XMM-NEWTON AND SUZAKU WE FOUND THAT THERE IS A HUGE RESERVOIR OF IONIZED GAS AROUND THE MILKY WAY WITH A MASS OF OVER 2 BILLION SOLAR MASSES AND A RADIUS OF OVER 100 KPC. THE BARYONIC MASS FRACTION OF THIS GAS IS CONSISTENT WITH THE UNIVERSAL VALUE. SIMILAR TO THE MILKY WAY OTHER SPIRAL GALAXIES SHOULD ALSO HAVE MASSIVE EXTENDED RESERVOIRS OF IONIZED HOT GAS IN THE CGM. SEARCHES OF SUCH A WARM-HOT GAS IN CGMS OF EXTERNAL GALAXIES HOWEVER HAVE GIVEN MIXED RESULTS. THERE ARE THREE SETS OF OBSERVATIONS WHICH ARE IN APPARENT CONFLICT: (1) CGMS AROUND NEARBY SPIRAL GALAXIES ARE APPARENTLY NOT EXTENDED (THIS MIGHT BE AN OBSERVATIONAL BIAS WHICH WE WILL TEST WITH THE PROPOSED PROGRAM); (2) CGMS AROUND MASSIVE SPIRALS ARE EXTENDED AND MASSIVE BUT GIVEN THE LARGE MASS OF THESE GALAXIES ABOUT AN ORDER OF MAGNITUDE HIGHER THAN THE MILKY WAY THE FRACTION OF BARYONS IN THE CGM IS STILL SMALL AND THE BARYONS ARE STILL MISSING; (3) THE MILKY WAY CGM IS EXTENDED AND MASSIVE AND MAY ACCOUNT FOR THE MISSING BARYONS. THEORETICAL MODELS SUGGEST THAT CGM PROPERTIES DEPEND ON GALAXY PROPERTIES SUCH AS THE GRAVITATIONAL MASS STELLAR MASS AND SPECIFIC STAR FORMATION RATE. SO TO UNDERSTAND THE PHYSICS OF GALAXY FORMATION AND EVOLUTION AND THE ROLE OF THE ACCRETION AND FEEDBACK MECHANISMS WE MUST PROBE THE ENTIRE PARAMETER SPACE OF THESE GALAXY PROPERTIES. GIVEN THAT CGMS OF GIANT MASSIVE GALAXIES HAVE BEEN STUDIED ALREADY IN THIS PROPOSED PROGRAM WE WILL STUDY GALAXIES WITH LOWER MILKY WAY-TYPE MASSES AND A RANGE OF STAR FORMATION RATE. OUR PROPOSED PROGRAM HAS TWO PARTS: (1) NEW OBSERVATIONS WITH SUZAKU (NOW ARCHIVED) AND (2) ARCHIVAL XMM-NEWTON OBSERVATIONS (1.09 MS). WE HAVE BEEN AWARDED 200KS OF SUZAKU TIME TO DETECT AND CHARACTERIZE THE WARM-HOT CGM IN A NEARBY LATE TYPE GALAXY NGC3221 WITH VERY HIGH SSFR. WE REQUEST SUPPORT FOR THE ANALYSIS OF THESE OBSERVATIONS. WITH OUR NOVEL XMM-NEWTON PROGRAM WE WILL PROBE THE RELEVANT PARAMETER SPACE OF STELLAR MASS STAR FORMATION RATE AND GRAVITATIONAL MASS OF GALAXIES. XMM-NEWTON HAS THE IDEAL COMBINATION OF LARGE FIELD OF VIEW AND LARGE EFFECTIVE AREA AT SOFT X-RAY ENERGIES WHICH IS CRUCIAL FOR FAINT DIFFUSE EMISSION STUDIES. WITH THE PROPOSED PROGRAM WE WILL DETECT AND CHARACTERIZE THE WARM-HOT CGM IN OUR TARGETS DETERMINE THEIR DENSITY PROFILES AND MEASURE THEIR MASS AND BARYON FRACTION. WE WILL PROBE AN EXTENDED PARAMETER SPACE OF GALAXY PROPERTIES TO UNDERSTAND HOW THE PROPERTIES OF CGMS DEPEND ON STELLAR MASS HALO MASS AND STAR FORMATION RATE OF GALAXIES. WITH THE PROPOSED STUDY WE WILL PRESENT THE BEST AND THE MOST COMPREHENSIVE PHENOMENOLOGICAL PICTURE OF THE CGM OF EXTERNAL GALAXIES WHICH WE WILL COMPARE WITH THEORETICAL MODELS OF GALAXY FORMATION. THIS WILL SIGNIFICANTLY ADVANCE OUR UNDERSTANDING OF GALAXY FORMATION AND EVOLUTION FEEDBACK AND METAL ENRICHMENT. THE PROPOSED STUDY IS RELEVANT TO THE NASA STRATEGIC GOAL TO DISCOVER HOW THE UNIVERSE WORKS EXPLORE HOW THE UNIVERSE BEGAN AND EVOLVED INTO ITS PRESENT FORM. THE PI'S EFFORTS TO INVOLVE UNDERGRADUATES FROM A COMMUNITY COLLEGE IN HER RESEARCH WILL IMPROVE RETENTION OF STUDENTS IN STEM DISCIPLINES BY PROVIDING OPPORTUNITIES AND ACTIVITIES ALONG THE FULL LENGTH OF THE EDUCATION PIPELINE (NASA STRATEGIC PLAN SUB-GOAL GOAL 6)., OUR MILKY WAY GALAXY, LIKE OTHER NEARBY GALAXIES, IS MISSING MOST OF ITS BARYONS (I.E. NORMAL MATTER). GALAXIES HAVE ALSO LOST MOST OF THE METALS THA
OpenAlex ID: W4367609813