Today will be an interesting day-from what I have read, the major trading surge occurs in the last 30 minutes of trading so a couple of million shares could trade in that time period.
I've done some research on other companies entering the Russell 2000 and the results are all over the place-some go down on this day. ICPT went up last year when it entered.
When I look at GALT's trading history the fact is that every time there is a major volume spike the stock goes strongly up, I am mostly expecting that today and a carry over to next week as well from the much higher company profile.
ICPT's announcement this week of a significant delay in their latest trial data report hasn't helped biotech's in the NASH space, I'm sure-ICPT is down about 20% from its recent highs.
The GALT chart (at least my version, based on 10/20/50/200 SMA and Bollinger Bands) is still strong so I think your estimate of $17-18 is reasonable.