1 00:00:03,430 --> 00:00:07,840 We saw what are the generic expectations in terms of observating galaxy formation, 2 00:00:07,840 --> 00:00:10,650 but now let's look at the observations themselves. 3 00:00:10,650 --> 00:00:15,732 How would we go about it? First we call the, most of the energy from 4 00:00:15,732 --> 00:00:21,738 young, forming galaxies, say... Brought the ellipticals would come from 5 00:00:21,738 --> 00:00:27,678 conversion of hydrogen to helium in stars adding up to about ten to the 60th ergs 6 00:00:27,678 --> 00:00:30,934 overall. And the question is then, what is the time 7 00:00:30,934 --> 00:00:36,046 interval over which this energy's released because what's observed is not energy but 8 00:00:36,046 --> 00:00:40,178 luminosity. So if we confine ourselves to the 9 00:00:40,178 --> 00:00:45,890 lifetimes of typical star bursts which are some tens of millions of years or maybe 10 00:00:45,890 --> 00:00:51,686 free fall time scale[UNKNOWN] ten to the eight years or maybe merger time scale ten 11 00:00:51,686 --> 00:00:55,255 to the nine years. We get roughly a range of luminosities 12 00:00:55,255 --> 00:00:59,264 that are between ten to the 11, ten to the 12 solar luminosities. 13 00:00:59,264 --> 00:01:06,290 And at the redshifts of interest that maps to apparent magnitudes of the order of say 14 00:01:06,290 --> 00:01:12,655 25 to 30 give or take depending on exact redshift and the luminosity of the actual 15 00:01:12,655 --> 00:01:16,134 protogalaxy. Few percent of that energy will emerge in 16 00:01:16,134 --> 00:01:19,980 form of emission lines, most notable lyman alpha if it's unobscured. 17 00:01:21,580 --> 00:01:24,846 And that will form a good way of finding galaxies. 18 00:01:24,846 --> 00:01:30,064 However, the big question is, is this luminosity obscured by dust in which case 19 00:01:30,064 --> 00:01:35,515 we have to look in the sub-millimeter, or just make a stellar photospheres in which 20 00:01:35,515 --> 00:01:40,808 case it emerges in rest from UV and will be observable in visible or near infrared 21 00:01:40,808 --> 00:01:44,430 light today. Seems that first there is no dust. 22 00:01:44,430 --> 00:01:51,791 At the very first stages we must be looking at unobscured galaxies. 23 00:01:51,791 --> 00:01:57,140 Emmission lines would then form a very good indicator of star formation at high 24 00:01:57,140 --> 00:02:01,714 redshifts and there are several ways in which we can do this. 25 00:02:01,715 --> 00:02:06,552 The simplest one is putting a dispersing element, like prism or grism, in front of 26 00:02:06,552 --> 00:02:10,710 the telescope optics, and so every source gets dispersed into its spectrum. 27 00:02:10,710 --> 00:02:16,488 That's called a slitless spectroscopy. This works for relatively bright objects 28 00:02:16,489 --> 00:02:21,146 from the ground at least because at any given pixel for a given spectrum you only 29 00:02:21,146 --> 00:02:24,194 get. Light from that wavelength, but you get 30 00:02:24,194 --> 00:02:27,874 light from all wavelengths from the background or foreground. 31 00:02:27,874 --> 00:02:33,122 So for really faint objects this will not work from the ground, although it has been 32 00:02:33,122 --> 00:02:36,177 done from space using Hubble Space telescope. 33 00:02:36,178 --> 00:02:40,259 An alternative is to use standard, long slit spectrograph. 34 00:02:40,260 --> 00:02:46,054 In which case a dispersed image of a narrow but long slit is being detected and 35 00:02:46,054 --> 00:02:51,386 that will work fine over a very small area in the sky but over a large area in a 36 00:02:51,386 --> 00:02:54,498 redshift. And because the light has been dispersed 37 00:02:54,498 --> 00:02:57,449 properly into sky subtraction, that's pretty good. 38 00:02:58,970 --> 00:03:03,640 Finally you can take a narrow band images, which band pass is very small. 39 00:03:03,640 --> 00:03:07,002 It will select emission lines of particular redshift. 40 00:03:07,002 --> 00:03:11,861 So it can go fairly deep, over reasonable area in the sky, as much as detector 41 00:03:11,861 --> 00:03:16,280 covers, but only over tiny redshift range. All of these have been used and all of 42 00:03:16,280 --> 00:03:20,484 them have produced some results. Narrow-band imaging has been very 43 00:03:20,484 --> 00:03:26,763 effective especially for looking for line and alpha line, of neutro hydrogen, the 44 00:03:26,763 --> 00:03:31,676 strongest unobscured[UNKNOWN] line. This is an example of the first high 45 00:03:31,676 --> 00:03:34,140 redshift galaxy found using that technique. 46 00:03:34,140 --> 00:03:39,172 It is a quasar companion redshift 3.2 and you can see in the bottom right image what 47 00:03:39,172 --> 00:03:43,075 it looks like in the light of line and alpha line[UNKNOWN]. 48 00:03:43,076 --> 00:03:47,380 The quasar in the middle, and its companion galaxy, off to the side, are 49 00:03:47,380 --> 00:03:51,234 very clearly seen. Yet, on the continuum image, just above 50 00:03:51,234 --> 00:03:55,090 it, the companion galaxy's just as faint as many others. 51 00:03:55,090 --> 00:03:59,698 So this is a good way to select emission line galaxies of high red shift, and it 52 00:03:59,698 --> 00:04:06,720 has been very productive so far. Another possibility is to just look on the 53 00:04:06,720 --> 00:04:10,010 long slit taking spectra of perhaps other objects. 54 00:04:10,010 --> 00:04:15,303 In this case here is a spectrum of quasar, that's the black streak in the top left, 55 00:04:15,303 --> 00:04:20,517 dispersed over some range of wavelength and off from it, away from it you seem an 56 00:04:20,517 --> 00:04:26,480 emission line that's attached. This is a background galaxy richer, 6.4, 57 00:04:26,480 --> 00:04:32,409 so, which is unrelated to the quasar. So it's pure chance that one finds objects 58 00:04:32,409 --> 00:04:35,600 like this. However, there is so many galaxies in the 59 00:04:35,600 --> 00:04:40,360 sky that this is not so crazy, and in fact a number of galaxies have been found using 60 00:04:40,360 --> 00:04:43,840 this technique. This is maybe not very efficient, but it's 61 00:04:43,840 --> 00:04:47,129 completely unbiased. Except of course for blind flux itself. 62 00:04:50,630 --> 00:04:55,796 Here is an example of one of the most distant if not the most distant galaxies 63 00:04:55,796 --> 00:05:00,798 selected using narrow band imaging, which are also confirmed using slit 64 00:05:00,798 --> 00:05:06,118 spectroscopy, this the [inaudible] of 7. The three images show 2 continuum images 65 00:05:06,118 --> 00:05:10,875 the galaxy light is diluted completely and the narrow banding which, you know, which 66 00:05:10,875 --> 00:05:14,292 it stands out because of it's strong Lyman alpha emission. 67 00:05:14,292 --> 00:05:21,236 The plot at the bottome shows the specturm that confirms that's indeed what we're 68 00:05:21,236 --> 00:05:24,645 looking at. A very popular technique that goes deeper 69 00:05:24,645 --> 00:05:27,338 then spectroscopy is the Lyman-Break imaging. 70 00:05:27,339 --> 00:05:31,367 We talked about that. In the context of galaxy evolution. 71 00:05:31,367 --> 00:05:36,988 Remember this works as follows. There is a strong continuum break at Lyman 72 00:05:36,988 --> 00:05:42,466 lifa or maybe a Lyman limit due to the intergalactic hydrogen or gas in galaxies 73 00:05:42,466 --> 00:05:45,638 themselves. And so if you have one filter blueward of 74 00:05:45,638 --> 00:05:48,359 that break, and at least two others redward. 75 00:05:48,360 --> 00:05:53,043 You can look for objects that look blue, or flat spectrum in the red, and then 76 00:05:53,043 --> 00:05:56,642 suddenly, very red, that is with a strong drop, the blue end. 77 00:05:56,642 --> 00:06:02,190 This is illustrated on the bottom with actual image from Hubble Space Telescope. 78 00:06:02,190 --> 00:06:07,026 Now, you can see the galaxy is well detected in three filters redward of the 79 00:06:07,026 --> 00:06:11,548 Lyman break. But is completely absent from the one 80 00:06:11,548 --> 00:06:16,412 that's lower than the Lyman break. This is a very effective way of finding 81 00:06:16,412 --> 00:06:20,512 high redshift objects. However, one has to trust that this is 82 00:06:20,512 --> 00:06:26,653 indeed the correct break and, usually, one would like to get confirming spectra to 83 00:06:26,653 --> 00:06:29,936 make sure. Here is an example of an object or 84 00:06:29,936 --> 00:06:36,008 actually two objects seen in Hubble ultra deep field where this technique has been 85 00:06:36,008 --> 00:06:39,584 applied. There are three detections, the huddled 86 00:06:39,584 --> 00:06:43,120 black points, and everything else is upper limits. 87 00:06:43,120 --> 00:06:49,096 What's drawn through this are couple model spectrum involving stellar populations, 88 00:06:49,096 --> 00:06:54,491 and it's probably obvious that more than one kind of spectrum can be used to fit 89 00:06:54,491 --> 00:06:57,850 these things. The authors go through certain arguments 90 00:06:57,850 --> 00:07:02,470 why should be in particular the one that corresponds to high redshift Lyman-Break, 91 00:07:02,470 --> 00:07:05,730 although obviously there is some uncertainty involved. 92 00:07:05,730 --> 00:07:11,457 If you believe that it's the high redshift object with a break that's been detected 93 00:07:11,457 --> 00:07:14,710 here. Then you estimate photometric redshifting, 94 00:07:14,710 --> 00:07:20,306 that's what's given here. At this time all of the galaxies beyond 95 00:07:20,306 --> 00:07:26,734 redshift seven or so have been detected using this technique. 96 00:07:26,734 --> 00:07:30,320 There are no spectroscopics confirmations so far because they're just to faint. 97 00:07:30,320 --> 00:07:35,117 We have to wait for the next generation of telescopes, say 30 meter telescope. 98 00:07:35,118 --> 00:07:39,619 And almost surely some of these really are at high redshifts, but it's possible, 99 00:07:39,619 --> 00:07:43,840 given the ambiguity of fitting models that some of those really are at lower 100 00:07:43,840 --> 00:07:48,530 redshift, maybe highly reddened galaxies, and so these have to be taken with a grain 101 00:07:48,530 --> 00:07:53,756 of salt. Here is a selection of such high-retro 102 00:07:53,756 --> 00:07:58,793 galaxy candidates from Hubble ultra-deep field and you can judge by yourself just 103 00:07:58,793 --> 00:08:04,218 how reliable these detections really are. They're estimated photo-metric redshifts 104 00:08:04,218 --> 00:08:09,176 are shown on the right, and indeed, they seem to always make an appearance in some 105 00:08:09,176 --> 00:08:14,886 red band but disappear in blue side. On the other hand, there is in addition to 106 00:08:14,886 --> 00:08:20,986 measurements of things, signals. There is a question of interpretation of 107 00:08:20,986 --> 00:08:24,907 fitting the correct stellar evolution model. 108 00:08:24,908 --> 00:08:29,250 Now assuming that this is actually correct, one can extend the modal plot. 109 00:08:29,250 --> 00:08:34,418 The history of Star formation and now we see that finally past about red shift four 110 00:08:34,418 --> 00:08:39,358 or five, the star formation density declines at high red shifts, which is what 111 00:08:39,358 --> 00:08:43,224 you expect. You begin with no galaxies whatsoever, you 112 00:08:43,224 --> 00:08:48,936 build them up, as we already know there is a fairly broad maximum or plateau of star 113 00:08:48,936 --> 00:08:54,732 formation history Down to redshift one or two and then decline towards the present 114 00:08:54,732 --> 00:08:58,420 day. So this makes sense and almost surely some 115 00:08:58,420 --> 00:09:04,812 of this is right although there may be some contaminants in these ostensible high 116 00:09:04,812 --> 00:09:10,306 redshift galaxy candidates. Another interesting thing happened, that 117 00:09:10,306 --> 00:09:15,896 some of these ostensible high redshift objects when observed in mid infrared 118 00:09:15,896 --> 00:09:21,830 shows some signal, which would correspond to somewhat older stellar population, 119 00:09:21,830 --> 00:09:27,334 maybe up to billion years old, meaning that they have to start very early on at 120 00:09:27,334 --> 00:09:33,010 very high redshift in order to have this evolved stellar component added to the 121 00:09:33,010 --> 00:09:36,497 brand new young stars that we normally look for. 122 00:09:36,498 --> 00:09:40,668 And finally how do we connect formational galaxies with that of large scale 123 00:09:40,668 --> 00:09:44,028 structures. You remember the idea behind biasing, that 124 00:09:44,028 --> 00:09:49,164 the first objects that form, form at the highest peaks of the density field. 125 00:09:49,165 --> 00:09:54,524 And so you expect that first galaxies will be strongly clustered in what will be 126 00:09:54,524 --> 00:09:59,881 cores of future clusters of galaxies. This is indeed seen we've seen companions 127 00:09:59,881 --> 00:10:03,379 of galaxies around quasars as well, it's in the field. 128 00:10:03,379 --> 00:10:08,051 And here is a set of Lyman alpha emission line galaxies that are on redshift of 129 00:10:08,051 --> 00:10:11,386 five. What's been seen in the cluster fairly 130 00:10:11,386 --> 00:10:15,358 strongly. Also the most distant quasars now past 131 00:10:15,358 --> 00:10:21,697 redshift of six or so, seem to show excess number of galaxies around them. 132 00:10:21,698 --> 00:10:26,380 Not always, and this is a very difficult obsrvation, but at least in some cases. 133 00:10:26,380 --> 00:10:30,579 And that fits very well with the idea of biased galaxy formation. 134 00:10:32,250 --> 00:10:40,138 Next we will turn to the Reionization Era at the frontier of modern observational 135 00:10:40,138 --> 00:10:41,304 cosmology.