G0.18-0.04 - Interaction of thermal and nonthermal radio structures in the arc near the galactic center

“THE GALACTIC CENTER ENVIRONMENT 651 Sgr A complex (Ekers et al 1983, Yusef-Zadeh & Morris 1987a, Pedlar et al 1989), which itself consists of three components: (a) the Sagittarius A West H II region and which is centered more or less on the central stellar cluster; (b) the somewhat larger-scale…”

“While there may still be other O-stars with less pronounced spectral features in the cluster, i.e. those still on the main sequence, it appears that the presently identified hot stars produce enough ionizing radiation to ionize the gas in the Sickle, even thought the geometry of the Sickle in relation to the cluster i…”

“12+0.02 and a cluster of HII regions (H1–H5) (Yusef-Zadeh & Morris 1987; Zhao et al. 1993).”

“3 superimposed on the VLA 20 cm image of the Galactic center by Yusef-Zadeh & Morris (1987), which shows the high MHD activity in the region with both thermal and non-thermal emission.”

“It is clearly seen at 20 cm to bifurcate into to at least two major strands (Yusef-Zadeh & Morris 1987a ; Yusef-Zadeh & Morris 1987b ; Lang et al. 1999b).”

“[1] Yusef-Zadeh, F.”

“The extension of the NRFs of the Arc toward positive latitudes has been argued to be physically associated with a lobe of polarized emission (Yusef-Zadeh and Morris 1987c).”

“18-0.04 (Yusef-Zadeh and Morris 1987) at l=10.6′, b=3′.”

“The group of compact sources located between SgrA and the Arched Filaments are labelled in Figure 1 as H1−H5, after Yusef-Zadeh & Morris (1987a) and are known Galactic center H II regions.”

“When approaching the SMBH, it looses mass through photo-evaporation due to the extreme flux of ionizing and FUV photons in the Galactic Center and due to tidal stretching.”

“Yusef-Zadeh & Morris (1987b), on the other hand, estimated the equipartition field strength in t e radio filaments at∼ 0.2 mG. Yusef-Zadeh & Morris (1987b) also provided an independent magnetic field strength estimate for the filaments of the Radio Arc with the help of a simple dynamical argument…”

“Furthermore, it has been suggested (Yusef-Zadeh & Morris 1987a, 1987b) that a uniform poloidal field permeates the central 50 pc.”

“These are thin, synchrotronilluminated structures running mostly perpendicular to the Galactic disc and characterized by very high magnetic field amplitudes, ∼mG (Yusef-Zadeh & Morris 1987; Morris & Yusef-Zadeh 1989).”

“However, the major axis of the structure function is tilted by roughly 708 with the Galactic plane, inconsistent with the large-scale poloidal field that has been inferred to exist in the inner 100 pc of the Galaxy (Yusef-Zadeh & Morris 1987a; Serabyn & Morris 1994).”

“They are believed to be manifestations of strong vertical field lines (mG strength), i.e., they are illuminated flux tubes in large-scale pervasive fields (Yusef-Zadeh & Morris 1987a; Uchida et al. 1996).”

“This is an order of magnitude lower than the estimates of ∼1 mG by Yusef-Zadeh & Morris (1987) along the giant Radio Arc (Yusef-Zadeh et al. 1984) and by Morris & Yusef-Zadeh (1989), who argued that milligauss magnetic fields pervade much of the volume of the CMZ.”

“18-0.04 is an HII region (the Sickle) and an intense photodissociation region (PDR) on the face of a molecular cloud adjacent to the massive Quintuplet star cluster (Yusef-Zadeh & Morris 1987; Nagata et al. 1990).”

“There is also evidence for strongGu sten magnetic Ðelds of D1 mG that permeate the area and are believed to suppress star formation (Yusef-Zadeh & Morris 1987c).”

“The central regions of galaxies, such as in the Milky Way, tend to have high interstellar pressures (∼ 5× 106 K cm−3; Spergel & Blitz 1992), strong magnetic fields (∼ 1 mG; Yusef-Zadeh & Morris 1987), and lower than expected star formation rate (Longmore et al. 2013).”

“The absence of any bending or distortion of the NTFs against the strong ram pressure of the GC molecular clouds indicates a field strength of about 1 mG (Yusef-Zadeh & Morris 1987a,b; see Chandran 2001 for further discussion of this point).”

“…central 250 pc of the Galaxy; the long (up to 50 pc) and narrow (<0.1 pc) synchrotron filaments show strong linearly polarized radio emission and have magnetic field orientations aligned with their long axes (Yusef-Zadeh & Morris 1987b; Yusef-Zadeh, Wardle & Parastaran 1997; Lang et al. 1999ab).”

“Secondly, our numerical model does not take the effects of magnetic fields into account, which may be of considerable strength in the Galactic centre (Yusef-Zadeh & Morris 1987, but also see Roy 2004 for lower estimates).”

“…are injected near one end and radiate as they stream at the Alfvén speed (e.g. Wentzel 1974), the observed filament lengths give a field strength of 1 mG for a length scale of 30 pc. Fields strengths of 1 mG have also been derived from dynamical arguments by Yusef-Zadeh and Morris (1987).”

“The ionized components of the gas are observed primarily via radio imaging, and a dominant feature in radio images of the Galactic center is Sgr A East, a nonthermal shell source of diameter D10 pc (Downes & Martin 1971 ; Yusef-Zadeh & Morris 1987a).”

“18−0.04) with the nonthermal radio filaments has prompted several groups to consider that gas in the H II regions might be ionized by the relativistic particles in the filaments (Yusef-Zadeh & Morris 1987; Serabyn & Güsten 1991).”

“The radio arc near the Galactic center (GC) ( 30 pc in projection from the dynamical center of the Galaxy, Sgr A ) is considered to be one of the most unusual collections of sources in the Galaxy (Yusef-Zadeh et al. 1984; Yusef-Zadeh & Morris 1987b; Morris & Yusef-Zadeh 1989).”

“This field strength corresponds to the large-scale field in the Galactic Centre (Yusef-Zadeh & Morris 1987; Morris & Yusef-Zadeh 1989; Crocker et al. 2010).”

“The high degree of polarization of the synchrotron emission from NRFs implies that their magnetic fields are highly ordered (Yusef-Zadeh & Morris 1987).”

“…compact sources have been reported in previous radio interferometer observations (not necessarily using the same frequency band as ours; e.g., Yusef-Zadeh & Morris 1987a; Forster & Caswell 2000; Lang et al. 2001; Lazio & Cordes 2008; Immer et al. 2012a; Rodríguez & Zapata 2013; Lu et al.…”

“The region’s spectacular non-thermal radio filaments (Yusef-Zadeh & Morris 1987) may be due to a fast outflow (e.g. Shore & LaRosa 1999).”

“Since magnetic pressure in these NTFs appears to overcome turbulent ISM pressure (otherwise, the NTFs would have bent due to interaction with molecular clouds), Yusef-Zadeh & Morris (1987a) derived a magnetic-field strength of about 1 milliGauss within these NTFs.”

“In general, the coherence of the NTFs over many parsecs in a region with a strong ram pressure from the surrounding molecular gas suggests that the magnetic field in these structures is quite strong (Yusef-Zadeh & Morris 1987a,b).”

“In the QPS region we Ðnd OB/KM D 0.66 (estimated errors are ^0.05 for all regions), in the E1 and E2 Ðlaments OB/KM D 0.53, in H1ÈH8, OB/ KM D 0.51 ; but in Sgr A East, OB/KM D 0.25, although the number of KM stars in Sgr A East is consistent with the other regions.”

“The presence of a ∼ 30 pc radio bubble and x-ray emission around the Quintuplet super-cluster system, east of the Sgr A ∗ , provides an example of how the 450-pc radio bubbles could be powered by star-forming regions in the disk (Yusef-Zadeh & Morris 1987; Sofue 2003; Ponti et al. 2015).”

“VLA observations reveal these sources to be peculiar HII regions with extremely filamentary morphology as well as complex velocity structure, although the coherence scale for the thermal filaments is much smaller than that of the NTFs (Yusef-Zadeh & Morris 1987b; Yusef-Zadeh, Morris, & van Gorkom 1987; Lang, Goss & Wo…”

“Indirect arguments on the arched filaments suggest that the field strengths may be as 1 http://trace.lmsal.com/ large as 1 mG (Yusef-Zadeh & Morris 1987) and the double helical filaments may also suggest the strong magnetic field (Morris, Uchida & Do 2006).”

“The strength of the magnetic field in the CMZ is estimated to be H ∼ 1 mG [H ∼ 1 mG from the magnetic field, “rigidity”, Yusef-Zadeh and Morris (1987); H ∼ 0.5 mG from the Zeeman effect of the H I line, Crutcher et al. (1996)].”

“Our Pα -derived extinctions are consistent with extinctions calculated in a similar manner by C00 using Br γ imaging along with 6 cm data from Yusef-Zadeh & Morris (1987).”

“In addition, the poloidal magnetic field of the Galactic center region is believed to be widely uniform and as strong as 1mGauss (Yusef-Zadeh & Morris 1987a, Yusef-Zadeh & Morris 1987b).”

“In previous radio observations, Yusef-Zadeh & Morris (1987) identified the Pistol nebula as the prominent pistol-shaped source at the center of Figure 1; it has a stellar source near its center of curvature, the Pistol Star (Figer et al. 1998; and references therein).”

“…synchrotron emission from the NTFs indicates that the magnetic field points along the filaments, whose apparent rigidity when they interact with molecular clouds and the turbulent interstellar medium suggests field strengths on the order of a few milligauss (see, e.g., Yusef-Zadeh and Morris 1987).”

“The elongated structures shown in Figure 5 might therefore be a component of the possible helical structure identified by Yusef-Zadeh & Morris (1987b).”

“The Arc, being nearly perpendicularly to the Galactic plane, was found to contain magnetic fields in the mG range, running almost parallel to its filamentary structure (Yusef-Zadeh and Morris 1987a, 1987b).”

“…invariant curvature of the filaments and their regularity (despite clear interactions with the turbulent GC ISM; Morris 2007) these structures must be quite rigid, which consequently allows the inference of a very large field strength of mG scale (Yusef-Zadeh & Morris 1987; Morris & Serabyn 1996).”

“The poloidal magnetic field of the Galactic center region is believed to be widely uniform and as strong as 1 mG (Yusef-Zadeh & Morris 1987a, 1987b).”

“…region of the Milky Way containing elevated molecular densities (10 3 – 10 6 cm − 3 ; e.g., Mills et al. 2018) and magnetic field strengths (100s of µ G – mG, Yusef-Zadeh & Morris 1987a; Chuss et al. 2003a; Pillai et al. 2015; Mangilli et al. 2019) compared to what is observed in the Galactic disk.”

“Also, radio studies have revealed a variety of thermal and nonthermal structures (e.g., Yusef-Zadeh & Morris 1987a, 1987b, 1987c).”

“The data were taken with the K band receiver (18.0−26.5 GHz) on 2012 January 14.”

“The unconvolved 1.4 GHz VLA total intensity data with an angular reso- Fig.”

“Their magnetic field strengths are estimated to be about 1 mG based on presumed stability of the filaments against ram pressure from ambient cloud collisions (Yusef-Zadeh & Morris 1987a, 1987b).”

“1 to be crossed by the Radio Arc as is also seen in maps at lower frequencies (Yusef-Zadeh & Morris 1987a; Ludovici et al. 2016).”

“…polarized synchrotron emission from the NTFs indicates that the magnetic field points along the filaments, whose apparent rigidity when they interact with molecular clouds and the turbulent interstellar medium suggests field strengths of the order of a few mG (see, e.g., Yusef-Zadeh & Morris 1987).”

“The Environment around N3: the Radio Arc NTFs and ”Wake” The two most prominent sources near (in projection) to N3 are the Radio Arc NTFs and the “wake” structure (Yusef-Zadeh & Morris 1987) (see Figure 1).”

“The rigidity of the magnetic field in the NTFs, as suggested bytheir smoothly varying and large-scale curvatures and the absence of significant deformations, led to an estimate of milligauss field strength within them (Yusef-Zadeh & Morris 1987a,b).”

“…observations near Sgr A* by Yusef-Zadeh et al. (1984), who noted a large arc-like formation to the northeast of Sgr A*. Subsequent studies of this region have shown a complex and detailed structure composed of thermal and nonthermal components (Yusef-Zadeh & Morris 1987; Morris & Yusef-Zadeh 1989).”