Molecular and R ecombination Lines in the C entral R egion of Sagittarius B2: REU a t NRAO During Summer Jason Curtis September 9; 2005

Size: px

Start display at page:

Download "Molecular and R ecombination Lines in the C entral R egion of Sagittarius B2: REU a t NRAO During Summer Jason Curtis September 9; 2005"

Domenic Ramsey
6 years ago
Views:

1 Mlelar and R embinatin Lines in the C entral R egin f Sagittaris B2: REU a t NRAO Dring Smmer 25 Jasn Crtis September 9; 25 Natinal Radi Astrnmy Observatry, Green Bank, WV ABSTRACT Dring the smmer f 25, I partiipated in the Researh Experiene fr Undergradates (REU) prgram at the Natinal Radi Astrnmy Observatry's (NRAO) Green Bank site. The prjet was fnded by a grant frm the Natinal Siene Fndatin. This paper presents the researh I ndted with Glen Langstn. We sed mapping bservatins made with the Rbert C. Byrd Green Bank Telespe (GBT) t stdy t he giant mlelar ld Sagittaris B2, whih is lated near the enter f r Milky Way Galaxy. My main wrk invlved develping sftware that takes these bservatins and prdes images f the bserved regin. 1. Intrdtin Dring the smmer f 25, I wrked with Glen Langstn n an bservatin prjet f the Sagittaris B2 (SgrB2) mlelar ld. This researh was dne as part f the REU prgram at the NRAO - Green Bank site, and was fnded by the Natinal Siene Fndatin. Sagittaris B2 is a giant mlelar ld lated relatively lse t the enter f r Milky Way Galaxy. It has an anglar size 1/3 that f the Mn. The tat tha.t it appears this large n the sky, and yet is s far away, shld give y a. sense that this is a big ld. This ld is nt what ne might think f when thinking f lds. It is nt simply a diffse grping f gas. Observatins made with the Very Large Array (VLA), have reslved ver 5 mpat COres within this ld. These res are sites f intense star frmatin, and ntain many high-lminsity stars. Srrnding these res is an extended envelpe f gas, whih ntains a rih mlelar hemistry. SgrB2 is atally e f the rihest and mst imprtant mlelar lds in the galaxy. Many mplex and imprtant mleles have been reently deteted by ther radi astrnmers sing the GBT. JResearh Experiene fr Undergradates at NRAO. Present address: University f Califrnia, Berkeley, 6] Campbell Hall, Berkeley, CA

2 - 2 My prjet invlved writing sftware in GBTIDL 2 that wld press and alibrate the raw data frm the bservatins made with the GBT, and allw the ser t prde maps f the bserved regin. 2. Observatins and Data Redtin On 24 Febrary 4, G. Langstn ndted mapping bservatins f SgrB2 with the 1m diameter Rbert C. Byrd Green Bank Telespe (GBT). These bservatins were made t test the GBT's apabilities fr wide band spetral srveys. Figre 1 shws the raw pwer spetrm f SgrB2. This is the raw data that we reeive frm the GBT telespe-reeiver system. It shws the intensity f the reeived signal verss freqeny. The bservatins were ndted in the GHz freqeny band. The next figre shws the raw pwer spetrm fr the mpat radi sre, Jl This sre is expeted t have a flat, featreless spetrm, yet it is fll f fltatins. These fltatins are artifiial spetral featres - they were nt prded by the astrnmial sre. Instead they are prded by the GBT's reeiver system. My firs t task is t remve these fltatins, minimize the nise, and remve and signal pwer frm SOres ther than SgrB Calibrating the Spetra The pwer Signal that is rerded is nt nly a prdt f the astrnmial sre nder bservatin, bt als ntains artifats frm the reeiving system as well. This nise an be anelled t by taking the pwer signal bserved while pinting n the SOre f interest, and sbtrating frm it the pwer signal f a psitin ff the sre. This will remve the largest nise fltatins that are dmiating r pwer spetrm, bt is nt qite sffiient fr identifying the real spetral lines, and prding maps f the bserved regin. We mplete the alibratin by perfrming a similar bservatin and allatin as abve, bt n a referene sre. Abve, I presented the pwer spetra f bth SgrB2 and anther sre, alled JI Ntie that these tw very different sres have nearly idential spetral strtre. This means that the fltatins in the spetra f these tw bjets are nt natral, bt are prded by the same phenmena in r reeiver system. This mean the ther sre an be sed as a referene Sre fr Or alibratin. We bserve it, and bserve a pstin nearby it, and then sbtrat the tw reslting pwer spetra, and btain a alibrated spetrm fr Jl Finally, we an divide these tw alibratins fr SgrB2 and JI This prdes a very nie pwer spetrm fr SgrB2, and is presented in Figre 3. 2GBTIDL is a. prgramming langage and system fr pressing data taken with the GBT. It is rrently being develped by NRAO n tp f the mmerially available IDL langage

3 Reslts f the Calibratin Ntie hw flat the alibrated spetrm f Figre 3 is, mpared t the raw spetra in Figre 1. The nise has been reded signifiantly. This has allwed the astrnmial spetral featres t emerge. These featres are the peaks, whih are emissin lines, and the dips, whih are absrptin lines. In this srvey, We have deteted 29 spetral lines tward SgrB2. Mst are emissin lines, and all bt ne f these are rembinatin lines f Hydrgen and Helim, whih I disss belw. We detet ne mlele in emissin, and it is Slfr Mnxide, SO. We als detet 9 absrptin lines frm varis mleles, inlding methanl (13CH3H), frmaldehyde (H 2 CO), and hydrxide (OH). We als reprt tw previsly ndeteted absrptin lines. The wild fltnatins n the left side f the plt, are dne t interferene frm satellite T.V. As y an see, these man-made radi Signals ttally dminate ver the very weak astrnmial signals. This example highlights the imprtane f the Natinal Radi Qiet Zne. If we did nt have sh a zne, it wld signifiantly limit what regins f the spetrm we are able t bserve, and therefre signifiantly limit what we are able t learn abt the niverse beynd the few freqeny bands that have been reserved fr astrnmial researh. Bak t the spetrnm, what is it we are lking at? Where d these peaks and trghs Cme frm? The majrity f the peaks are a partilar kind f emissin line alled rembinatin lines. These rembina tin lines are prded in the regin srrnding ht stars. In the Intrdtin, I mentined tw imprtant fats: first, SgrB2 is a giant ld f gas; send, it ntains many mpat res with ht and yng stars. These stars are emitting energeti phtns, whih inize the gas srrnding them. Hydrgen is made p f ne prtn and ne eletrn. When the phtn interats with the hydrgen atm, it an knk the eletrn t f the hydrgen system, leaving jst the prtn. vvhen the eletrn rejins with the prtn, rembinatin lines are emitted. The same thing happens fr Helim, Carbn, and the ther atms that make p the gas srrnding these stars. Figre 4 shws a Hydrgen rembinatin line, alled Ha, next t a Helim rembinatin line, Hea. Amng ther things, mparing the strengths f these lines an aid in the stdy f their abndane in the ld. Next, let's lk at Figre 5. These are absrptin lines prded by the mlele frmaldehyde, H2CO. The plt is zmed in t highlight the weaker absrptin featmes, bt the main spike, whih is mainly t ff, an be seen mpletely in Figre 3. S we an see three separate absrptin featres. What is interesting, is that these are nt prded by different presses. It is the same mlele, nderging the same transitin, that has prded these three different absrptin featres. They are entered at slightly different freqenies bease they are atally assiated with different lds. These lds are eah mving at a different velity. The velity shifts the freqeny arding t the Dppler Shift Eqatin, /:',f=f (1 )

4 - 4 where 61 is the hange in freqeny, f is the bserved freqeny, v is the velity f the sre, and is the speed f light. S, nt nly are we able t stdy the bjet f interest, bt we an als learn abt the galati strtre that lies alng t he line f sight between s and the galati enter. 3. Taking Pitres f the Center f r Milky Way Galaxy Or mapping bservatins were made with the GBT in t he fllwing manner. A regin was determined, srrnding the entral psitin f the sre. The telespe pints at ne rner, and takes data. It then sans in a snake-like pattern arss the bserving regin, stpping at eah interval t take data. Or map is a 1' x 1' regin, whih is rghly 1/3 f t he anglar size f the mn. It is mpsed f 3 x 3 different bserving latins. I begin by perfrming t he alibratin desribed abve n all 9 psi tins. When we lk at anything with r eyes, we are seeing an image prded by r brain that is mpsed f all the light that falls within the visible prtin f the spetrm f light. The maps that are presented here are nt mpsed f the intensity f the light ver a r ange f freqenies, bt instead are prded by taking t he intensity at a speifi freqeny. I desr ibed abve an example f hw atms and mleles emit light at a partilar freqeny, depending n hw they are "exited" by phtns emitted by nearby stars and ther sres. Prding images f the bserved regin at a partilar freqeny allws astrnmers t stdy hw that partilar atm r mlele is distribted in the bserved regin, and hw it is interating with the rest f the regin. The next step in prding maps, t herefre, is seleting whih freqeny we wld like t image. I mst say here that there are atally tw different types f maps that I will present. I have desribed spetral line maps, whih shw the intensity f the emissin thrght the regin. T he ther type f map is a ntinm map. Lk bak at Figre 3. Ntie hw the emissin lines are nt entered at zer intensity, bt instead ar e fnd n tp f a brad emissin, tha t is rghly flat ver r freqeny band. This brad emissin featre is alled ntinm emissin. When we see absrptin lines, it is this ntinm emissin being absrbed by intervening mleles alng the line f sight. Three maps are presented as examples f my smmer wrk. Figre 6 shws the ntinm emi ssin at 1444 MHz, and is nifrm ver r entire bserved fr eqeny band. The ntr lines that are verlaid n the image, represent lines f eqal intensity. The lines are drawn at.5,.1,.25,.33,.5,.66,.75, and.9 x the maximm ntinm intensity f the regin. The image in Figre 7 repres ent the intensity f Ha emissin. The ntrs are t he same ntinm trs frm Figre 6. T his map shws that the Ha rembinatin emissin has the

5 -5 same spatial distribtin as the ntinm emissin. The image in Figre 8 represents the intensity f SO, slfr mnxide, emissin. The ntrs represent Hae emissin, and are spaed at the same fratin f maximm intensity as the ntinm ntrs f the previs images, thgh nw in relatin t the peak Hae emissin. This map shws that SO des nt have the same spatial distribtin as Hae. Instead, the SO emissin is mre entrally nentrated. 4. Smmary This smmer, I nentrated n writing sftware, in GBTIDL, that wld allw the ser t prde alibrated maps f the giant mlelar lnd, Sagittaris B2. I investigated a nmber f alibratin tehniqes, and fnd ne that wld minmize the nise, and allw fr the prdtin f ntinm and spetral maps. I then trned my attentin t writing a nmber f prgrams that wld alibrate all the mapping bservatins, and allw the ser t prde maps at partilar freqenies, with ntrs f ther transitins verlaid. This was my first experiene wrking with a researh-lass telespe and at a siene lab. Nt nly did I learn a great deal abt the mlelar ld SgrB2, and radi astrnmy in general. I als learned many skills that will have brad appliatin t whatever field f astrphysial researh I deide t prse. 5. Aknwledgements First, I am gratefl fr the finanial spprt prvided by the Natinal Siene Fndatin. The REU prgram is exellent and it plays an imprtant rle in training the next generatin f researh sientists. I wld als like t thank Glen Langtn fr ating as my advisr, and wrking with me thrght the smmer. Finally, I wld like t thank the Natinal Radi Astrnmy Observatry, and everyne at the Green Bank site, fr hsting me and prviding a wnderfl and edatinal smmer researh experiene.

6 <D 1 >, Sa n 15 V. RADI-OBS FO 13.7 GH z Pl : Tsys: 1. 1' Int 29.5 Fsky GHz IF: Teal : 2.66 Langstn LS T BW 8. MHz TGBT3C26 N d , C r, [: L. Az: 172. EI: 22, 8 HA: -,56,a 4 rl-, ,--,--,--.--,-,--,--,--.--,-,--.--,--,- 3 lfj C 2.' 1 Y U , 14,5 LS R Freqen y (GH z) 1J, - 1J Q. i{l ; - ' 1J. -..: E-<...,- ( tfj Q. > : 1J bd > tfj " I 15, , Th Ag 18 15:52: : ",-,..,

7 Sa n 13 V. RADI- OBS FO 13.7 GHz Pl: Tsys: Int Fsky GHz IF : Tea l: 2.56 Langs tn LST BW 8. MH z TGBT3C26 Nd a;? j"!-7 :S.,/ Az: EI 38.3 HA: -.36 Jl ,--,-,--,-,--,--,--,-.--,--.-,--,--.-,--,--.-,--,--,-, ,-, 1:l k : 2.5 I' 2; I III 1:l C -(J). I " U '., LSR Freq eny ( GHz ) Th Ag 18 15:48:22 25 it 1:l k. k :S k..8 k :,.q E-<.; k "ti bl en. k >r:.. ] ill k ;> en k N. ",,.q +'

8 :a San 15 V RADI - OBS FO 13.7 GHz Pl: LL Tsys " Int 29.5 Fsky GHz IF Teal: 2.66 Langstn LST BW 8. MHz TGBT3C_26 Nd ] --, '--'.,..."",,, :,'..' ; <UI Az 172. EI: 22 8 HA: II 3 iii 111l, I II I r ] I OJ. r x t. " if] 2 r Q = "... ". "ti " " " if] I g LSR Freqen y (GHz ) M :a r..... U... N ". "3 Te Ag 9 11: 47 : f...< '

9 "" > - '-.../ > 1 (f) 25.8 Sa n 15 V - 62 RADI-OBS FO Int 29.5 Fsky Langstn LST: BW [.-, )\)1\ l / \ 25.4 <lj x :J ;: , I, ; r---- I 13.7 GH z GHz 8. MHz v Pl: LL IF: 3 TGBT3C26 I, " LSR Freqeny (GHz)._aDC Tsys: Tea l: Nd Of) C Cd Az: 172. EI: 22.8 HA -.56 "Ij "',j/\\ /--//- \ I \ I \) Te Ag 16 17: 39: ;:>.s = :a." " i. ] p:) SC U W N"Ij ;.: :. N p:), 1l :..::l

10 San 15 V - 62, RAD I- OBS FO 137 GHz Pl: LL Tsys: Int 29,5 Fsky : 14,59961 GHz IF : 3 Tal: 3,21 Langstn LST : ,2 8W 8. MHz TG8T3C26 Nd,-." r- ' ":" (..-,.J / Az: 172. EI: 22.8 HA: -, > >: 27. -<f) OJ x ::J 26.5 LL J I ) J \ \.'-.../' _/-_/ , C "".::: a d'.;;; " '5.S " <l.8 s:: ::: :I: "d <:l :I: N.. rn"" 14, n LSR Freqeny (GHz) T e Ag 16 17:53:28 25 i:;;

- 11 2 1. 6 4 N -:> E L C 2 C - 2 > 11:' 1.8-4 4 2-2 -4 Re la tive R.A. in are min (J2) Fig. 6.- SgrB2 Map: The image is ntinm emissin at 1444 MHz.

11 N -:> E L C 2 C - 2 > 11:' Re la tive R.A. in are min (J2) Fig. 6.- SgrB2 Map: The image is ntinm emissin at 1444 MHz. The ntr lines represent the same ntinm emissin, at.5,.1,.33,.5,.66,.7, and.9 x the peak intensity. The referene bar is in nits f Janskys.

12 N --, E L 2 C C. U ill ill.2: ill r: Relative RA in armin - 2 (J 2) - 4 Fig. 7.- SgrB2 M ap: The image is Ha rembinatin emissin. The ntr lines represent the ntinm emissin, at.5,.1,.33,.5,.66,.7, and.9 x the peak intensity. The referene bar is in nits f Janskys.

13 N -, 2 E L C C -2 > r Relative R.A. In ar min (J2) -4. Fig. 8.- SgrB2 Map: The image is slfr ltinxide, SO, emissin. The ntr lines represent the H a: emissin, at.5,.1,.33,.5.66,.7, and.9 x the peak intensity. The referene bar is in nits f Janskys.

To get you thinking...

To get you thinking... T get yu thinking... 1.) What is an element? Give at least 4 examples f elements. 2.) What is the atmic number f hydrgen? What des a neutral hydrgen atm cnsist f? Describe its "mtin". 3.) Hw des an atm